Sacrificial Anode

An anode made of suitable metal placed in a water heater tank to protect the tank from corrosion. Anodes of metals such as aluminum, magnesium, or zinc are sometimes installed in water heaters and other tanks to control corrosion of the tank. The introduction of the anode creates a galvanic cell in which the magnesium or zinc will go into solution (be corroded) more quickly than the metal of the tank, thereby imparting a cathodic (negative) charge to the tank metal(s) and thus preventing tank corrosion.     This corroding of the anode metal is called "the sacrifice of the anode".


Condition of exposure under which there is a "practical certainty" that no harm will result in exposed individuals.

Safe Drinking Water Act (SDWA)

The national legislation first passed by the U.S. Congress and signed into law by the President in 1974 and amended in 1986. The SDWA directs the U.S. Environmental Protection Agency to promulgate and enforce standards for safe drinking water necessary to protect public health at public water systems serving 25 or more people for an average of 60 days per year. The law also contains provision for delegating primary enforcement responsibility to states and for protecting underground sources of drinking water.

Safe Water

Water that does not contain harmful bacteria, or toxic materials or chemicals.   Water may have taste and odor problems, color and certain mineral problems and still be considered safe for drinking.

Safe Yield

The annual quantity of water that can be taken from a source of supply over a period of years without depleting the source beyond its ability to be replenished naturally in "wet years."

Sal Marina

Spanish name for sea salt.


A hydrometer which measures the percent of salt as NaCl in brine or other salt solutions. A 100 percent reading on a salimeter is about 26.4 percent salt by weight at 60 degrees F. Some people use the term "salinometer" to refer to a salimeter.


Consisting of, or containing, salt.

Saline Solution

Any solution with the total dissolved solids (TDS) usually ranging from 15,000 to 30,000 mg/L.     For example, a solution of sodium chloride and water, usually containing other salts also.     May also be called saline water.


The relative concentration of dissolved salts, usually sodium chloride, in a given water. A measure of the concentration of dissolved mineral substances in water.


An instrument for determining the salt concentration (salinity) of brine water by measuring the electrical conductivity of the solution.     A salinometer is sometimes called a salt gauge.


See Salimeter.


1. (chemistry) A chemical compound formed by the neutralization of an acid with a base. For example, H2SO4 (acid) + 2NaOH (base) = NaSO4 (salt) + 2H2O (water).

2. (water treatment) compounds such as sodium chloride (NaCl) or potassium chloride (KCl), both of which are used in solution to regenerate cation exchange water softeners and some dealkalizers.

3. common table salt, which is sodium chloride (NaCl).

SEE ALSO common salt (NaCl); rock salt; solar salt; water softener salt.

Salt Block

Evaporated salt or fine rock salt which is mechanically compressed into dense blocks, weighing about 50 pounds each, which are sometimes used in residential water softeners.

Salt Bridging

The creation of salt encrustment and cementing together of salt particles in dry storage brine tanks which causes tight bonding of the entire salt mass to the walls of the brine tank and prevents the salt from dropping into the incoming water for brine makeup.

Salt Cake

Sodium sulfate (Na2SO4) which is only 90-99 percent pure (i.e., contains 1-10 percent of substances other than Na2SO4).     Salt cake is made by heating rock salt with sulfuric acid, producing muriatic acid and salt cake.

Salt Dosage

See Regeneration Level.

Salt Efficiency

In an ion exchange water softener, the hardness removal capacity calculated as grains of hardness removed divided by the weight of salt in pounds that is used to achieve that amount of hardness reduction.     Operational salt efficiency refers to the salt efficiency performance of a water softener under conditions of actual or simulated long term use (six months or more) in a household where gallons of water usage typically varies from day to day.

Salt Mushing

See Mushing.

Salt Splitting

An ion exchange process in which neutral salts in water are converted to their corresponding acids or bases.    A strong base anion exchanger resin can convert a salt solution to caustic (base) (for example, NaCl + ROH = RCl + NaOH); and a strong acid cation exchanger can convert a salt to acid (for example, NaCl + HR = NaR + HCl).

Salt Splitting Capacity

A regular test used on an ion exchange resin to determine the capacity of a used resin versus the standard rated capacity of the resin when fresh.

Salt Water

The general term for all water over 1,000 ppm (mg/L) total dissolved solids.

Fresh Water - <1,000 TDS

Brackish - 1,000-5,000 TDS

Highly Brackish - 5,000-15,000 TDS

Saline - 15,000-30,000 TDS

Sea Water - 30,000-40,000 TDS

Brine - 40,000-300,000+ TDS

Saltless (or salt free) Water Softener

SEE saltless water treatment device; water softener

Saltless (or salt free) Water Treatment Device

A device, product, or equipment using chemical, physical or any other means, to counteract scale buildup of hard water minerals (calcium and magnesium) without the use of salt for regeneration. Depending on the scale reduction or prevention method other effects of soft water may also be observed. SEE ALSO water treatment; water treatment device; water softener; water softening.


Soil particles between 0.05 and 2.0 mm in diameter.

Sand Filter

The oldest and most basic filtration process, which generally uses two grades of sand (coarse and fine) for turbidity removal or as a first stage roughing filter or prefilter in more complex processing systems.     Municipal water treatment systems often used gravity rapid-rate sand filters. Pressure-type sand filters plus coagulants are used for commercial applications.     For home use or for small swimming pools, a pressure sand filter is also used.

Sand Trap

A mechanical device to separate fine sand or other abrasive material from water in wells with faulty screens. The hydrocyclone separator is one form of a sand trap.

Sanitary Sewer

A sewer that transports only waste waters (from domestic residences and/or industries) to a waste water treatment plant.

Sanitary Survey

An on-site review of the water source, facilities, equipment, operation, and maintenance of a public water system for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water.


The act of sanitizing. Sanitization is not an absolute phenomenon; it is a partial removal or inactivation of microorganisms.   Depending on the system, a sanitization operation should reduce the viable organism population by 50 to 99.9 percent, but it should completely eliminate enteric pathogen-related organisms such as Salmonella and E. coli.     (Disinfection by comparison, should reduce 99.9 to 99.9999 percent of viable microorganisms.)


To reduce the number of bacterial contaminants to safe levels as judged by public health requirements. To make clean and free or inactivation of dirt, filth, and conditions injurious to health.     Generally considered to reduce germ count by 50 to 99.9 percent.     The USEPA requires that sanitizing claims must show a 99.9 percent microbial reduction in five minutes.


An agent that results in the reduction of bacterial numbers to accepted public health limits by sanitizing. Sanitizers are applied in the cleaning operations of inanimate objects.


Organisms living on dead or decaying organic matter. They help natural decomposition of organic matter in water.

Saturated Solution

A solution which contains the maximum amount of the dissolved substance (solute) that a solution of this kind can normally hold at this temperature.

Saturated Zone

The area below the water table where all open spaces are filled with water.


In water chemistry, means the state of a solution (water) when it holds the maximum equilibrium quantity of dissolved matter at a given temperature and pressure. The limit when no more of a given substance will dissolve.

Saturation Index

A scale showing the relationship of calcium carbonate to the pH and hardness of a given water. The saturation index is commonly used to determine the scale-forming tendency of a particular water.


A device which produces a fluoride solution for the fluoridation process. The device is usually a cylindrical container with granular sodium fluoride on the bottom. Water flows either upward or downward through the sodium fluoride to produce the fluoride solution.


A coating or precipitate deposited on surfaces such as kettles, water pipes, or steam boilers that are in contact with hard water.     Waters that contain carbonates or bicarbonates of calcium or magnesium are especially likely to cause scale when heated.     Also called hard water scale.


In water treatment applications, a polymer matrix or ion exchanger that is used specifically to remove organic species from the feedwater before the water is to pass through the deionization process.


Cubic feet of air per minute at standard conditions of temperature, pressure, and humidity (0 degrees C/14.7 psia/50% relative humidity).

Schedule, Pipe

A sizing system of arbitrary numbers that specifies the I.D. (inside diameter)and O.D. (outside diameter) for each diameter pipe.  This term is sued for steel, wrought iron, and some types of plastic pipe.  Also used to describe the strength of some types of plastic pipe.

Screen Size

See Mesh Size.


Silt Density Index.


See Safe Drinking Water Act.


(SECK-key) Disc - A flat, white disc lowered into the water by a rope until it is just barely visible.  At this point, the depth of the disc from the water surface is the recorded seechi disc transparency.

Secondary  Drinking Water Regulations

See Drinking Water Standards.

Secondary Treatment

As relates to waste water treatment, the process which makes up the second step in treating waste water and removes suspended and dissolved solids and biochemical oxygen demand (BOD) from the waste water which has already undergone primary treatment.

Sediment Yield

The quantity of sediment arriving at a specific location.

Sedimentary Rock

Rock that results from the consolidation of layers of loose sediment made up of various kinds of organic and inorganic matter.

Sedimentary Rock

Rock that results from the consolidation of layers of loose sediment made up of various kinds of organic and inorganic matter.


The process of suspended solid particles settling out (going to the bottom of the vessel) of water that has little or no movement.     Sometimes sedimentation only occurs after the particles have begun to coagulate (either naturally or because of the use of a coagulant aid such as alum) into larger and heavier flocs.


The percolation of water through the soil from unlined channels, ditches, water courses, and water storage facilities.

Seize Up

Seize up occurs when an engine overheats and a part expands to the point where the engine will not run.     Also called "freezing."

Selective Ion Exchanger

An ion exchange medium which shows selectivity. For example, a chelating ion exchange resin which will remove only gold ions from solution.


The tendency of an ion exchanger to "prefer" (have more attraction for) certain kinds of ions over others, as if the resin were ranking the types of ions in order to be removed: most preferred ion, second most preferred, etc.

Selectivity Band

The respective region or zone within an ion exchanger or adsorption medium bed where individual ions or substances accumulate and are removed from the water in order of their individual respective preferences for the medium.     Because different substances each have different affinities or selectivity preference for the treatment medium, removal occurs in different zones of the medium bed.     The zone for the ion or substance with the lowest selectivity will proceed through the bed first, and the zone for the highest selectivity substance will proceed through the bed last.

Seltzer Water

See Soda Water.


Semiconductor Equipment and Materials International.

Semiconductor Equipment and Materials International (SEMI)

The group which has set the electronics grade purified water standards.

Semiconfined Aquifer

An aquifer that is partially confined by a soil layer (or layers) of low permeability through which recharge and discharge can occur.

Semipermeable Membrane

See Membrane.


An electrical or electronic device which measures the quality of the product water leaving the treatment cycle.     A sensing meter which measures conductivity or resistivity (resulting from TDS) is used for deionization, electrodialysis and reverse osmosis.     In a cation water softener, sensors used are either as:     electronic devices which measure hardness in effluent softened water, or   probes which detect the slightly different electrical impedance between that caused by calcium/magnesium and sodium ions.   The sensor is immersed in the resin bed and triggers regeneration.


An electrical or electronic device which measures the quality of the product water leaving the treatment cycle.     A sensing meter which measures conductivity or resistivity (resulting from TDS) is used for deionization, electrodialysis and reverse osmosis.     In a cation water softener, sensors used are either as:     1. electronic devices which measure hardness in effluent softened water, or   2. probes which detect the slightly different electrical impedance between that caused by calcium/magnesium and sodium ions.   The sensor is immersed in the resin bed and triggers regeneration.


An electrical or electronic device which measures the quality of the product water leaving the treatment cycle.  A sensing meter which measures conductivity or resistivity (resulting from TDS) is used for deionization, electrodialysis and reverse osmosis.  In a cation water softener, sensors used are either as:  1. electronic devices which measure hardness in effluent softened water, or 2. probes which detect the slightly different electrical impedance between that caused by calcium/magnesium and sodium ions.  The sensor is immersed in the resin bed and triggers regeneration.


A spiral-wound membrane element or cartridge used in cross flow membrane systems.


A diseased state caused by the presence of pathogenic microorganisms in the bloodstream.


The liquid and semisolid contents removed by pumping from a septic tank.


A condition produced by bacteria when all oxygen supplies are depleted. If severe, bottom deposits appear and water turns black, gives off foul odors, and the water has a greatly increased chlorine demand.

Septic System

An on-site system designed to treat and dispose of domestic sewage; a typical septic system consists of a tank that receives wastes from a residence or business and a system of tile lines or a pit for disposal of the liquid effluent that remains after decomposition of the solids by bacteria in the tank.

Septic Tank

A tank (usually underground) into which the solid matter of household sewage flows and is held for decomposition caused by bacteria.     Septic tanks are common in rural areas where no municipal sewage system is available.


Bacteria multiplying in the bloodstream.

Sequential Actions

One action occurring after or followed by others in a given order--as opposed to simultaneous actions.


To keep a substance (e.g., iron or manganese) in solution through the addition of a chemical agent (e.g., sodium hexametaphosphate) that forms chemical complexes with the substance.  In the sequestered form, the substance cannot be oxidized into a particulate form that will deposit on or stain fixtures.  Sequestering chemicals are aggressive compounds with respect to metals, and they may dissolve precipitated metals or corrode metallic pipe materials.

Sequestering Agent

1. A chemical that forms complexes with metallic ions in solution so that the metallic ions may no longer be precipitated.  For example, calcium soap precipitates are not produced from hard water treated with sodium hexametaphosphate.  Note however, the tendency for condensed phosphate polymers, such as hexametaphosphates, may be to hydrate in water, especially under conditions of high temperature or high pH, and thereby revert to a more simple and stable phosphate form, such as orthophosphate which can no longer sequester the hardness and metal ions. 2. Any agent that prevents an ion from exhibiting its usual properties because of close combination with an added material.


A chemical reaction in which certain ions are bound into a stable water-soluble compound so that they (ions) are prevented from certain normal but undesirable actions.   For example, the sequestration of iron to prevent it from oxidizing, precipitating, and staining.  The same as sequestering.  SEE ALSO chelation.

Serial Filtration

The arrangement of two or more filtering steps, one following the other, in order to remove increasingly finer particulates at each stage and provide for filtration of all sizes of suspended solids.     Cartridge-style units often employ this method, using depth prefilters (compressed fibers) followed by surface filtration with a micromembrane cartridge element.

Service Flow

The rate in U.S. gallons per minute (gpm) or liters per minute (L/min) at which a given water processing system can deliver product water. The rating may be for intermittent peak flow or constant flow.

Service Line Sample

A one-liter sample of water collected in accordance with CFR Section 141.86(b)(3) of the code of Federal Regulations, that has been standing for at least six hours in a service line.

Service Pipe

The pipeline extending from the water main to the building served or to the consumer's system.

Service Run

That portion of the operating cycle of a water processing system during which the water is actually being treated. The other portion of the cycle is regeneration.    For example, that portion of the cycle in which the hard water supply is passed through a regenerated and rinsed bed of ion exchange material, thereby producing soft water.

Service Unit

A term most often applied to portable exchange tanks.


Attached firmly to a permanent base and not free to move about.     Bacteria grow and multiply faster when attached (sessile) in water systems, than when free-floating (planktonic) in water. Attached sessile cells form a larger colony; their polysaccharide containing glycocalyx slime layer helps adhere other bacteria cells and nutrients which float past and also acts as a protective layer which resists chemical disinfectant penetration.     This sessile microbial colonization is known as biofilm in water systems.

Set Point

The position at which the control or controller is set.     This is the same as the desired value of the process variable.


The combination of liquids or water carrying wastes from homes, businesses, institutions, and industries.     In some cases, storm water, groundwater, and surface water may be included in the sewage flow. In the larger sense, sewage is the water supply of a community after the water supply has been used.


An underground system of conduits (pipes and/or tunnels) that collect and transport waste waters and/or runoff; gravity sewers carry free-flowing water and wastes; pressurized sewers carry pumped waste waters under pressure.

Sewerage System

The network of sewers that carries sewage from point of origin to point of treatment.

Shallow Well

A well sunk in easily-penetrated ground to a point which is below the water table but usually less than about 30 feet in depth.

Shearing Action

The action of low temperature water flowing at high rates which splits and separates particle agglomerations and prevents the formation of floc deposits during the coagulant feed/filtration process.     This action may also tear away from the filter any previous deposits or suspended matter.


The separation and insulation of metal parts of a pipe joint by a special fitting which will not conduct electric current.     The fitting prevents corrosion caused by galvanic action between two different metals.     Shielding can also be a protective cover or barrier that prevents transmittance of heat or radiation to or from a component of water treatment equipment.

Shock Load

The arrival at a water treatment system of raw water containing unusual amounts of algae, colloidal matter, color, suspended solids, turbidity, or other pollutants.

Short Circuiting

A condition that occurs in tanks or basins when some of the water travels faster than the rest of the flowing water.     This is usually undesirable since it may result in shorter contact, reaction, or settling times in comparison with the theoretical (calculated) or presumed detention times.

SI System of Units

The International System (SI) of units that was adopted and recommended for use in science and technology by the 11th General Conferece on Weights and Measures in 1960.     This coherent system of units is built from the following seven SI base units:     <b>Physical    Name of SI Unit   Symbol for</b>  <b><u>Quantity                   SI Unit</u></b>     length          meter            m     mass            kilogram         kg     time            second           s     electric        ampere           A   current     thermodynamic   kelvin         K   temperature     amount of       mole           mol   substance     luninous        candela        cd   intensity

Siemens (S)

Formerly called mho.     The siemens (S) is the SI unit of conductance equal to the reciprocal of the ohm.

Sievert (Sv)

The SI unit of ionizing radiation dose equivalent.     One sievert (Sv) equals 100 rems.


As used in water chemistry, a collective term encompassing all reactive (dissolved) and inert (nonreactive and undissolved or colloidal) forms of the chemically resistant dioxide SiO2 of silicon, or silicates formed from silicon and oxygen in combination with one or more other minerals or metals.  Silica, such as quartz for example, is present in almost all earth's minerals, rocks, soils, sands, and clays.  It is found in fresh water in a range of 1 to 100 mg/L.  In a laboratory water analysis report, silica is nearly always identified as silicon dioxide (SiO2), however when dissolved in water silica is actually hydrated to silicic acid (SiO2nH2O) and associated anions.  Below a pH of 9, silica is present mostly in the silicic acid form (SiO2  2H<sub>2</sub>O, also written as H4SiO4.  At low pH, silicic acid can polymerize or condense to form uncharged colloid particles (known as colloidal silica) as small as 0.02 microns in size.  As the pH of water exceeds 8, silicic acid (H4SiO4) increasingly dissociates into the bisilicate anions H3SiO4- and H2SiO42-.  This will increase the solubility of the silica unless divalent and polyvalent cations are available in significant concentrations.  These cations of calcium, magnesium, iron, and aluminum, for example, will likely cause precipitation of insoluble silicate salts, especially at higher pH levels.  The precipitation of multivalent cations with the silicates tends to occur at a pH value of 1 to 2 points below the point at which the cation hydroxide solubilities would be exceeded.  Silicates can interfere with the crystal growths of precipitating metal and mineral cations thereby keeping such silicate complexed particulates in the colloidal size ranges, e.g., silicates are a contributor to formations of colloidal iron and colloidal manganese.    Below pH 8, dissolved silica in the silicic acid form (H4SiO4) precipitates to SiO2 when the solubility of silicic acid is exceeded.  Precipitated silica and silicates can be very difficult to redissolve.  Silica concentrations above 100 mg/L in reverse osmosis waste streams (concentrate water) may cause silica deposition which will foul the membrane, however because silica is slow to crystalize some RO systems can operate safely with silicic acid concentrations as high as 140 mg/L in the RO concentrate without experiencing silica scale formation.  The potential for silica precipitation should be evaluated whenever silica is present in an RO feedwater at a concentration above 20 mg/L.  Silica is also objectionable in boiler feedwater because it may form a tenacious scale in the boiler itself, and because it volatilizes at high temperatures and redeposits on turbine blades.  High concentrations of silica are likewise a concern in cooling tower makeup water because of the characteristic uncertainty about silica's solubility limits.    Inorganic silicate compounds, such as soluble sodium silicates (the simplest form of glass, known as water glass) have been employed for more than 70 years to treat water.  These silicates are anodic corrosion inhibitors that will combine (react with) the free metal released at the anode site of corrosion activity in copper, lead, cast iron and ferrous metals, steel, galvanized steel, bronze, red and yellow brass, and nickel alloys, to form an insoluble metal-silicate compound which seals off the corrosion site.  Relatively high dosages, 25 to 50 mg/L, of silicate are required during the first 30 to 60 days of treatment.  This should form the initial protective coating for corrosion control.  Thereafter, the silicate dosage is reduced incrementally to maintenance feeds in the 4 to 10 mg/L range.  There are reports of preferences of sodium silicate corrosion inhibitors for successful treatment of low alkalinity and


A group of compounds containing oxygen and silica(SiO2).  Silicates are considered anodic corrosion inhibitors combining with the free metal released at the anode site of corrosion activity and forming an insoluble metal-silicate compound.  Silicates can also be used to sequester soluble iron and manganese present in source water to help prevent oxidation and the formation of red and black water.


Soil particles between 0.05 and 0.002 millimeter in approximate diameter.

Silt Density Index (SDI)

A test used to measure the level of suspended solids in feedwater for membrane filtration systems.     The test consists of the time it takes to filter 500 milliliters of the test water through a 47-millimeter diameter, 0.45 micron rated microporous filter under a constant pressure of 30 psig.     The SDI of feedwater to a reverse osmosis membrane should be maintained at less than 5, preferably less than 3.3.     SDI = 100 (1-t<sub>1</sub>/t<sub>2</sub>)/T    where:     t<sub>1</sub> = time to filter 500 mL of   water initially,   t<sub>2</sub> = time to filter 500 mL of water after T minutes (T is usually 15 minutes.)


To reproduce the action of some process, usually on a smaller scale.

Single Family Structure

A building constructed as a single-family residence that is currently used as either a residence or a place of business.

Single-Stage Pump

A pump that has only one impeller. A multistage pump has more than one impeller.

Single-Stage Recirculation

(reverse osmosis) Process used in a multiple (2-6) membrane reverse osmosis system in which a portion of the concentrate stream is split off and routed back to the inlet and mixed with the feedwater.     This increases the flow across the membrane without increasing the amount of feedwater and increases the overall recovery rate. The pump capacity will affect the amount of water to be recirculated and the recovery rate.

Single-Stage System

(reverse osmosis) A reverse osmosis system in which the water is passed through the membrane(s) only once by using a single high-pressure pump.


A place in the environment where a compound or material collects.


To react calcium oxide (lime or quicklime) with water to form calcium hydroxide (slaked or hydrated lime) plus heat.


The slope or inclination of a trench bottom or a trench side wall is the ratio of the vertical distance to the horizontal distance or "rise over run."

Slotted Lateral Pipes

Underdrain lateral pipes which have many tiny openings (as though they had been partially cut around the perimeter with a hacksaw) instead of orifices (drilled 1/4 in. or 3/16 in. holes.)


The action of a medium (filter, ion exchanger, or membrane) casting off into the effluent stream any substance intended for removal from the water.     Sloughing may be caused by shearing action or by ion selectivity.

Slow Rinse

1. (ion exchange) That portion of the rinsing stage which usually follows the introduction of the regenerant and during which the rinse water (deionized, decationized, softened, or untreated water) passes through the resin at the same flow rate as the regenerant;    2. (filtration) The initial rinse down after application of regenerant for resettling the medium bed. After the bed is resettled, a final fast rinse is used to "purge" the bed.

Slow Sand Filtration

A process involving passage of raw water through a bed of sand at low velocity (generally less than 0.4 m/h) resulting in substantial particulate removal by physical and biological mechanisms.


The settleable solids separated from water during processing.


A temporary abnormally high concentration of an undesirable substance which shows up in the product water.     A slug is generally a symptom of a malfunction of the water processing unit.     For example, a "slug" of iron-rust might appear due to the shearing action of a high-demand flow which loosens a previously deposited iron precipitate.


A watery mixture or suspension of insoluble (not dissolved) matter; a thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).

Small Bore Piping

Copper or stainless-steel pipe with a small diameter of 0.5 inches or 15 mm.     Such pipe is commonly found in pump-assisted hot water central heating systems.


Secondary Maximum Contaminant Levels. Secondary MCLs for various water quality indicators are established to protect public welfare.


Suggested No Adverse Response Level.  The concentration of a chemical in water that is expected not to cause an adverse health effect.


The water-soluble reaction product of a fatty acid ester and an alkali (usually sodium hydroxide) which produces suds when used with water for washing or cleaning purposes.     Some soaps are mild disinfectants. Common soaps such as sodium and potassium soaps are soluble but can be converted to insoluble calcium and magnesium soap "curds" (bathtub rings) by the presence of hardness ions in the water.

Soap Curd

The insoluble precipitate that forms when soap is used in hard water.  Soap curd and lime soap are synonymous


synthetic organic chemicals.

Soda Ash

(Na2CO3) A common water treatment chemical, sodium carbonate, which is used for pH modification, as an alkaline builder in some soaps and detergents, and in the lime-soda ash water softening process.

Soda Water

Water which has been impregnated with carbon dioxide (CO2) so that it will be effervescent when not under pressure. Same as carbonated water, seltzer water, and sparkling water.


(Na+) A metallic element found abundantly in compounds in nature, but never existing alone.     Sodium compounds are highly soluble and do not form curds when used with soaps or detergents.     Many sodium compounds are used in the water treatment industry. Most notable is the use of sodium chloride as a regenerant in the cation exchange water softening process.

Sodium Bicarbonate

(NaHCO3) A mild alkali, commonly called baking soda.     Sodium bicarbonate is used in powdered hard surface cleaners and some presoak formulations to provide alkaline cleaning at a controlled level.

Sodium Carbonate

(Na2CO3) A fairly strong alkaline salt occurring naturally as soda ash.     A solution of sodium carbonate (soda ash) may be used with a simple proportionate chemical feed pump system to raise the pH of a water supply. Each mg/L of carbon dioxide in water requires a minimum of 2.5 mg/L of soda ash for neutralization.     Sodium carbonate finds wide use as a builder in laundry detergents and as a source of alkalinity in powdered hard surface cleaners and presoak products. Sodium carbonate supplies alkaline cleaning power and also softens water by precipitating the hardness minerals out of solution.     It is also called soda ash and is available on the retail market in a hydrated crystalline form under the name "washing soda."

Sodium Chloride (NaCl)

The chemical name for common table salt.     Sodium chloride is also widely used for regeneration of ion exchange water softeners and in some dealkalizer systems.

Sodium Citrate

The sodium salt of citric acid.     Sodium citrate sequesters hardness minerals and is used as a builder in some nonphosphate products. Its principal application is in liquid laundry detergents; it also is used in some presoak products.

Sodium Cycle

The cation exchange water softening process in which sodium ions in the resin are exchanged for hardness ions in the water.     Sodium chloride is commonly used for resin regeneration.

Sodium Hexametaphosphate

A glassy sodium polyphosphate used as a sequestering, dispersing, deflocculating agent and as a coating agent to form a thin passivating film that protects metals from corrosion.

Sodium Hexametaphosphate

A substance that has a molecular ratio of 1.1 parts of sodium monoxide (Na2O) to 1 part of phosphorus pentoxide (P2O5, with a guaranteed minimum of 76 percent P2O5.  Several specialized compositions are available.  It is also called sodium polyphosphate or glassy sodium phosphate, and is used as a sequestering, dispersing, deflocculating agent and as a coating agent to form a thin passivating film that protects metals from corrosion.

Sodium Hydrosulfite

(Na2S2O4) A crystalline salt which is a strong reducing agent and the main ingredient in several resin cleansers that are used to clean iron-fouled ion exchange resin beds.

Sodium Hydroxide (NaOH)

A strong alkaline compound used as a regenerant for anion exchange resin in deionization systems and for the pH modification of low pH (acid) water. Sodium hydroxide is also called caustic, caustic soda, or lye>.

Sodium Hypochlorite (NaOCl)

Liquid bleach; used as a source of chlorine in water treatment.     Laundry bleach available from grocery stores is 5.25 percent chlorine and commercial strength bleach available from swimming pool suppliers or chemical companies is usually 12.5 percent chlorine.

Sodium Metaphosphate

Any of several complex phosphates with excellent sequestering properties.

Sodium Silicate(s)

(Na2SiO2 or SiO2,Na2)  Glassy polymeric silicates used to prevent corrosion by formation of a thin passivating film on metal surfaces in boilers and other water systems.

Sodium Tripolyphosphate

(Na5P3O10) A crystalline salt used chiefly as a water softener, sequestering agent, and deflocculating agent, especially in soaps and detergents.

Soft Water

Water which contains less than 1.0 grain per gallon (<17.1 milligrams per liter (mg/L) or parts per million (ppm)) of total hardness. SEE ALSO hard water; hardness.

Softened Water

Water which has been treated by any method that reduces its total hardness content to less than 1 gpg (17.1ppm). SEE ALSO hard water; zero soft water; soft water.

Software Programs

Computer programs; the list of instructions that tell a computer how to perform a given task or tasks.

Soil Erodibility

A measure of the soil's susceptibility to raindrop impact, runoff, and other erosional processes.

Soil Profile

A vertical section of the earth's highly weathered upper surface often showing several distinct layers or horizons.

Soil Sealant

A chemical or physical agent that plugs porous soils and prevents leaching or percolation.

Soil Sealant

A chemical or physical agent that plugs porous soils and prevents leaching or percolation.

Soil Structure

The arrangement of soil particles into aggregates.

Soil Texture

The proportions of soil particles (sand, silt, and clay) in a soil profile.

Solar Salt

Common salt which is produced by solar evaporation in shallow ponds or lagoons and used in water softener regeneration.


A metallic compound used to seal the joints between pipes.     Until recently, most solder contained 50 percent lead. The use of lead solder containing more than 0.2 percent lead is now prohibited for pipes carrying potable water.

Sole Source Aquifer

An aquifer that supplies 50 percent or more of the drinking water of an area.


A magnetically (electrical coil) operated mechanical device.     Solenoids can operate a small valve or a switch.

Solenoid Shutoff Valve

An electrical device operated by a magnetic coil to make the valve either open for flow or close to shut off water flow.     This type of valve is used extensively for flow control and direction on many water processing systems.


(In water and waste water laboratory analyses) The matter dissolved or suspended in water or waste water.


The substance which is dissolved in the solvent (generally a liquid such as water) to form a solution.


A mixture in which one or more substances (solutes) are dissolved into another substance (solvent), usually a liquid, in such a way that the solute is equally distributed (homogeneous) throughout the solvent in the form of either molecules (as in a sugar solution) or ions (as in a salt solution).


A liquid substance that dissolves another substance (the solute) to form a solution.


A surface phenomenon which may be either absorption or adsorption, or a combination of the two; often used when the specific mechanism is not known.

Sounding Tube

A pipe or tube used for measuring the depths of water.

Sour Brine

Brine that contains a high concentration of calcium, magnesium, or other substances that would interfere with its use or reuse for effective regeneration of exhausted ion exchange resin.


The scale or range of values an instrument is designed to measure.


A perforated pipe in an aerator or ozone contact compartment through which the air or ozone-containing air is sprayed into the water, and which allows for the diffusion of the air or ozone into the water.

Specific Conductance

A rapid method of estimating the total dissolved solids (TDS) content of a water supply.     Its measurement indicates the capacity of a sample of water to transmit an electrical current, which is associated with the concentration of ionized substances in the water. An alternate method is the measurement of <i>specific</i> (electrical) <i>resistance</i>.     The unit of measure for specific conductance is siemens (formerly called mhos) per centimeter which is 1.0 divided by specific resistance. When the numbers get too small, the microsiemens (S) is used.     For example, 100 mg/L of NaCl dissolved in water causes a specific conductance of 212 microsiemens per centimeter, whereas a 1,000 mg/L solution of NaCl in water would result in 2,000 microsiemens per centimeter.     It is well known that pure water is a very poor conductor of an electric current. However, when ionizable compounds (salts, etc.) are dissolved in the water, the solution becomes a conductor of electric current. The nature of the ionized compound and the amount of it dissolved are responsible for the specific conductance (or specific resistance) of the solution.     The more salts dissolved, the greater is the specific conductance.

Specific Gravity

Weight of a particle, substance, or chemical solution in relation to the weight of water.     Water has a specific gravity of 1.000 at 4 degrees C (39 degrees F).     Particulates in raw water may have a specific gravity of 1.005 to 2.5.

Specific Resistance

The capacity for resisting the flow of electrical current.     In the case of liquids, such as water, specific resistance is the resistance of a 1.0-centimeter cube, which is the resistance offered by the liquid between two electrode plates 1 cm. square and placed 1 cm. apart.     The unit of measure is ohms-centimeter, and specific resistance is the reciprocal of specific conductance.     One hundred milligrams per liter of NaCl dissolved in water causes a specific resistance of 4,716 ohms-centimeter, whereas a 1,000 mg/L solution of NaCl in water would result in 500 ohms-cm.

Specific Yield

The quantity of water that a unit volume of saturated permeable rock or soil will yield may be expressed as a ratio or as a percentage by volume


A chemical analytical instrument used in spectroscopy.


A technique used in chemical analyses which is based on the principle that many substances, when crossed by a beam of light, allow a unique and well-defined fraction of that light to pass or emit a well-defined fraction of radiation when returning from an atomic vapor state to their fundamental state.     The characteristic wave length pattern of the absorbed or emitted light can be used to identify the particular substance with great certainty.     The quantity of the light absorbed or emitted is proportional to the concentration of the substance.     Spectroscopy is one of the most frequently used analytical methods for water analyses. Ultraviolet light (UV) spectroscopy (using light wave lengths between 10 and 390 nanometers) and infrared (IR) spectroscopy (using light wave lengths between 780 and 300,000 nanometers) are used particularly to identify and quantify organic molecules. Atomic absorption spectroscopy (AA) is used to identify and quantify inorganic elements.     Spectroscopy is also called spectrometry and spectrophotometry.


The measure of the bead roundness or "whole bead" count of beads in an ion exchange resin product or other bead form absorbent or filter medium.


A very common construction configuration for one style of reverse osmosis membrane and cartridge filter element.     In RO membranes, the membrane sheets are assembled in layers around a perforated mandrel product water tube, with coarse mesh spacer screens between the layers, to form a complete module element.     In cartridge filter elements, the filtration material, such as fiber cord, is continuously wound around a perforated mandrel core tube.

Split-Stream Treatment

The art of proportionally blending a stream of treated water with a stream of untreated water from the same source to achieve a lower measurement of a given contaminant in the blended stream, thus not removing all of the contaminant but still meeting the water quality desired, such as meeting a maximum contaminant level requirement for delivered water.     Split-stream operation makes it possible to treat less than the full flow of water.


Excavated material such as soil from the trench of a water main.


A small reproductive body, often single-celled, capable of reproducing the organism under favorable conditions.     The spore is sometimes considered the resting stage of the organism. Among the organisms that may produce spores are algae, bacteria, and certain protozoans.     In water, most spores resist adverse conditions which would readily destroy the parent organism.


An agent that destroys microbial spores. By definition, sterilizing agent.


A place where groundwater flows naturally from the soil or rock formation onto the land surface or into a body of surface water.     A spring is sometimes used as a source of water for a shallow dug well.

Spring Line

Theoretical center of a pipeline. Also, the guideline for laying a course of bricks.

Spring Water

Water obtained from an underground formation from which water flows naturally to the surface or would flow naturally to the surface if it were not collected underground.


The ability of an ion exchange product or filter medium to withstand physical and chemical degradation in cycle-after-cycle operations.

Stainless Steel (ss)

A chromium alloy with substantially 50 percent or more iron and usually with some nickel (typically 12 to 30 percent chromium and zero to 22 percent nickel) that is practically inert toward rusting and corrosion.     The nickel content of ss contributes to improved corrosion resistance. Austenitic stainless steel contains 16 to 26 percent chromium, six to 22 percent nickel, low (less than 0.15 percent) carbon, and cannot be hardened by heat treatment; ferritic ss contains 15 to 30 percent chromium, low (0.1 percent) carbon, and cannot be hardened by heat treatment; martensitic ss contains 12 to 20 percent chromium, controlled carbon and other additives, and can be hardened by heat treatment which increases the tensile strength from 80,000 to 200,000 psi.    = ADD TABLE HERE =


A physical or chemical quantity whose value is known exactly and is used to calibrate or standardize instruments.

Standard Industrial Classification (SIC)

The statistical classification standard published by the United States Office of Management and Budget (OMB) that assigns an industry number to businesses and business units by type of economic activity.     It is the classification standard underlying all establishment-based Federal economic statistics classified by industry type.     The system uses from a one-digit to a four-digit classification number depending on how narrowly the business unit is defined. There are 11 one-digit groupings and over 1,000 four-digit groupings.     Household and industrial water treatment equipment manufacturing, for example, is in SIC 3589, water conditioning service is in SIC 7389, distribution of water conditioning equipment is in SIC 5074, manufacturing of fluid power control valves is in SIC 3492, manufacturing of water treatment chemicals is in SIC 2899, manufacturing of distilled water is also in SIC 2899, manufacturing of pharmaceutical water or of water purification tablets is in SIC 2834, manufacturing of carbonated and flavored bottled water is in SIC 2086, bottling natural, spring, or mineral water is in SIC 5149, and retailing bottled water is in SIC 5499.

Standard Methods

A shortened title for the Standard Methods for the Examination of Water and Wastewater, a joint publication of the American Public Health Association, American Water Works Association, and the Water Pollution Control Federation.     This widely-used volume outlines the procedures used to analyze water and waste water impurities and characteristics.

Standard Methods for the Examination of Water and Wastewater

A joint publication of the American Public Health association, American Water Works Association and the Water Pollution Contol Federation which outlines the procedures used to analyze the impurities in water and waste water.

Standard Sample

The aliquot of finished drinking water that is examined for the presence of coliform bacteria.

Standard Solution

A solution in which the exact concentration of a chemical or compound is known.


To compare with a standard.    In chemistry, to find out the exact strength of a solution by comparing it with a standard of known strength, or   to set up an instrument or device to read a standard.   This allows you to adjust the instrument so that it reads accurately or enables you to apply a correction factor to the readings.


Chemically, starch refers to complex carbohydrates obtained from vegetable sources.     In home laundry usage, the term has been expanded to cover products that perform the same function as starch, i.e., supplying body or stiffness to fabrics, but that are based on synthesized chemicals such as carboxymethylcellulose or polyvinyl acetate. The latter are called synthetic or plastic starches.     Vegetable starch comes as:     dry, uncooked starch (lump, cube, or powder), which must be mixed with hot water or cooked before use;  pre-cooked flakes, which can be mixed with cold water;   a concentrated pre-cooked solution; and   a concentrated solution in an aerosol container for spraying directly on fabrics while ironing.   Synthetic or plastic starches come as liquids and in aerosol form for direct application. The liquids are available in soluble form, which is removed in the next laundering. More durable varieties last through several washes.     Besides supplying body and stiffness, starch gives ironed articles a fresh smooth appearance, helps garments stay clean longer because of the harder, smoother surface, and facilitates soil removal in the next wash since the soil becomes imbedded in the starch, not the fabric.


Devices used to start up large motors gradually to avoid severe mechanical shock to a driven machine and to prevent disturbance to the electrical lines (causing dimming and flickering of lights).


The agency of the State or Tribal government which has jurisdiction over public water systems.     During any period when a State or Tribal government does not have primary enforcement responsibility pursuant to Section 1413 of the Safe Drinking Water Act, the term "State" means the Regional Administrator, U.S. Environmental Protection Agency.


Fixed in position; resting; without motion.

Static Head

When water is not moving, the vertical distance (in feet) from a specific point to the water surface is the static head.     (The static pressure in psi is the static head in feet times 0.433 psi/ft.)

Static Pressure

The static pressure in psi is the static head in feet times 0.433 psi/ft.    The static pressure in psi is the static head in feet times 0.433 psi/ft.

Static System

A system or process in which the reactants are not flowing or moving.

Static Water Depth

The vertical distance in feet from the center line of the pump discharge down to the surface level of the free pool while no water is being drawn from the pool or water table.

Static Water Level

The elevation or level of the water table in a well when the pump is not operating.   The level or elevation to which water would rise in a tube connected to an artesian aquifer, or basin, or conduit under pressure.


That portion of a machine which contains the stationary (non-moving) parts that surround the moving parts (rotor).

Steady Operating Flow Rate

The flow in U.S. gallons per minute (or liters per minute) at which a water processing filter or ion exchanger will deliver its rated capacity.     For water softeners, this flow is based upon delivering softened water from an incoming raw water of 20 grains per gallon total hardness as calcium carbonate.

Stepwise Regeneration

The method of regenerating ion exchange resin beds several times with the same regenerant, but at a higher concentration each time.     The method is usually used to avoid calcium sulfate precipitation when sulfuric acid is employed as a regenerant for cation bed units of deionizer systems that are being used to decationize unsoftened feedwater.


The removal or destruction of all (or greater than 99.9999 percent of all) microorganisms, including pathogenic and other bacteria, vegetative forms and spores.


Complete (100 percent or at least greater than 99.9999 percent) destruction or inactivation of all living organisms.     The USEPA requires that sterilization claims must demonstrate killing or inactivation of all microorganisms, including bacterial spores.


An instrument used to magnify sounds and convey them to the ear.


Based on the assumption that the actions of a chemical substance results from probabilistic events.


Related to the proportions in which chemicals combine to form compounds and the weight relations in chemical reactions.     Stoichiometry is the mathematical and theoretical study of how chemicals combine.

Stokes Law

A formula for calculating the rate of fall of particles through a liquid medium.     The rate at which a spherical particle will rise or fall when suspended in a liquid medium varies as the square of the particle's radius, as the density of the particle, and as the viscosity of the fluid.

Storage Capacity

The maximum volume of water available for use from the water storage tank, e.g., the amount available from a RO or distiller water storage tank.

Storage Tank

A compartment used to accumulate the product water from a water treatment unit so sufficient quantity and/or pressure is available for intermittent periods of higher flow rate water use.

Storm Sewer

A sewer that collects and transports surface runoff to a discharge point (infiltration basin, receiving stream, treatment plant).


The formation of separate layers (of temperature, plant, or animal life) in a lake or reservoir.     Each layer has similar characteristics such as all water in the layer has the same temperature.

Stratified Bed

In ion exchange applications, a bed in which two exchangers of different classes and different densities have been placed in the same column (bed), such as weak base anion resin on top of a strong base anion exchanger, or in cation exchange systems, a weak acid on top of a strong acid resin.

Stray Current Corrosion

Corrosion due to electrical current flowing through paths other than the intended circuit. This form of electrolysis causes corrosion independent of other environmental factors like pH and is proportional to the Amperage of the applied current. This type of corrosion typically causes a concentration of localized pitting. Stray current can originate from many sources, including: Cathodic protection systems, welding operations, improper grounding of radio transmitters, grounded DC electric sources, and faulty electrical appliances.

String Wound Element

A cartridge-style filter element constructed by continuous spiral winding of natural or synthetic yarn around a preformed product water tube core and then building it up in layers to form a depth-type filter element.

Strip Cropping

A crop production system that involves planting alternating strips of row crops and close-growing forage crops; the forage strips intercept and slow runoff from the less protected row crop strips.

Strong Acid Cation Exchanger

A cation exchange resin with an exchange site/active group (usually sulfonic) capable of splitting neutral salts (NaCl, MgSO4, Ca[NO3]2, etc.) to form their corresponding free acids (HCl, H2SO4, HNO3, etc.).

Strong Base Anion Exchanger

An anion exchange resin with an exchange site/active group [usually quaternary amine, -N(CH3)+++] capable of splitting neutral salts (NaCl, CaSO4, KNO3, etc.) to form their corresponding free bases (NaOH, Ca[OH]2, KOH, etc.).


(C8H8) A fragrant, liquid, unsaturated hydrocarbon used chiefly in the manufacture of synthetic rubber, resins, and plastics.     Styrene is the prime ingredient in many cation and anion exchange resins.


Of intermediate duration, usually used to describe studies or levels of exposure between five and 90 days.

Submerged Aquatic Vegetation (SAV)

Aquatic vegetation, such as sea grasses, that cannot withstand excessive drying and therefore live with their leaves at or below the water surface.     SAVs provide an important habitat for young fish and other aquatic organisms.


The distance between the water surface and the media surface in a filter.

Submersible Pump

A pump designed to fit inside the well casing and to operate below the water level in a drilled well.

Submicron Filter

A cartridge-type membrane filter used in fine particle separation applications to remove particulates of less than one micron in size.

Suction Lift

The negative pressure [in feet (meters) of water or inches (centimeters) of mercury vacuum] on the suction side of the pump.     The pressure can be measured from the center line of the pump down to (lift) the elevation of the hydraulic grade line on the suction side of the pump.

Sulfate Bacteria

Sulfate-reducing bacteria, such as Desulfovibrio, and the single-celled aerobic sulfur-oxidizers of the genus Thiobacillus.     The sulfate-reducing bacteria contribute to tuberculations and galvanic corrosion of water pipes and to hydrogen sulfide taste and odor problems in water. Thiobacillus, by its production of sulfuric acid, has contributed to acid corrosion of metals.

Sulfonic Acid

(-SO2OH) A specific acidic group which forms the exchange site active group in certain cation exchange resins and gives these resins their ion exchange capability.

Sulfur (S)

A yellowish solid chemical element.     "Sulfur" is also often used to refer to sulfur water.

Sulfur Water

Water containing objectionable amounts of hydrogen sulfide gas which causes an offensive "rotten egg" odor.

Sulfuric Acid

(H2SO4) A very strong, corrosive and hazardous acid used as a regenerant for the cation stage of an ion exchange deionization system.     Sulfuric acid is also used occasionally to lower the pH of highly alkaline water.     When higher concentrations of sulfuric acid are combined with high concentrations of calcium, calcium sulfate crystals precipitate and create tenacious fouling of media particles.     An older name for sulfuric acid is oil of vitriol.


The addition of excess amounts of chlorine to a water supply to speed chemical reactions or ensure disinfection within a short contact time.     The chlorine residual following superchlorination may be high enough to be unpalatable, and thus dechlorination is commonly employed before the water is used.


Federal law which authorizes USEPA to manage the cleanup of abandoned or uncontrolled hazardous waste sites.


Liquid removed from settled sludge.     Supernatant commonly refers to the liquid between the sludge on the bottom and the water surface of a basin or container.

Supersaturated Solution

An unstable condition of a solution (water) in which the solution contains a substance at a concentration greater than the saturation concentration for the substance.

Supplier of Water

Any person who owns or operates a public water system.

Support Media Bed

Material of a specific graded particle size (such as gravel) used as a subfill to support the primary medium bed.     In larger diameter systems (tanks), this bed improves the collection of processed water and promotes more uniform distribution of the backwashing water.

Surface Filtration

Filtration that occurs at the surface layer (as opposed to within the body depth) of the filter and is accomplished by passing the material to be filtered over a grating, screen, sieve, or membrane fabric with microsized holes.     The size of the holes in the filter determines what materials will pass through and what will be filtered out (held back).

Surface Loading

One of the guidelines for the design of settling tanks and clarifiers in treatment plants.     Used by operators to determine if tanks and clarifiers are hydraulically (flow) over- or underloaded.     Also called overflow rate.

Surface Pump

A mechanism for removing water or waste water from a sump or wet well.

Surface Runoff

Precipitation, snow melt, or irrigation in excess of what can infiltrate the soil surface and be stored in small surface depressions; runoff is a major transporter of nonpoint source pollutants.

Surface Tension

The tendency of a liquid to form a relatively tough "skin" or film on its surface.     Surface tension is caused by the attraction between the molecules of the liquid, and it is surface tension that causes water molecules to stick together and form drops. Surface tension makes it possible to float a razor blade on the surface of a glass of water even though the blade is much heavier than the water.     The surface tension that holds the drops together makes it difficult for the water to penetrate or "wet" fabrics (or skin). Soaps and detergents contain "wetting agents" to reduce surface tension and increase fabric penetration by water.

Surface Water

All water naturally open to the atmosphere (rivers, lakes, reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other collectors which are directly influenced by surface water.


A surface-active substance that when added to water lowers surface tension and increases the "wetting" capabilities of the water. Reduced surface tension allows water to spread and to penetrate fabric or other substances to be washed or cleaned.     There are three categories of surfactants: detergents, wetting agents, and emulsifiers.     "Surfactant" is a contraction for surface-active agent.

Surge Chamber

A chamber or tank connected to a pipe and located at or near a valve that may quickly open or close or a pump that may suddenly start or stop.     When the flow of water in a pipe starts or stops quickly, the surge chamber allows water to flow into or out of the pipe and minimize any sudden positive or negative pressure waves or surges in the pipe.

Suspended Solids

Solids that either float on the surface or are suspended in water or other liquids, and which are largely removable by laboratory filtering.   The quantity of material removed from water in a laboratory test, as prescribed in Standard Methods for the Examination of Water and Wastewater.

Sweet Brine

Brine that contains sufficient sodium or potassium content and is relatively low in calcium, magnesium, or other interfering substances such that it is effective for use or reuse in regenerating exhausted ion exchange resin.

Sweet Water

Fresh water. Palatable water. Not salt water.


The expansion of certain ion exchange resins when converted into a specific ionic state.     This is a reversible expansion, as the resin may well shrink as it becomes exhausted. Some exchangers will expand as they exhaust.     Cation exchange water softening resins will generally swell when exhausted (loaded with hardness ions) and will shrink when regenerated with heavier salt dosages of 10 to 15 pounds of sodium chloride (NaCl) or potassium chloride (KCl) per cubic foot of resin.     Standard cation softening resin (8 percent polystyrene/DVB), in the calcium form, will shrink about 5 percent in volume when treated with a 25 percent salt-brine solution.


The combined action of several chemicals which produces a greater effect than would be obtained by simply adding together the effects produced by each chemical separately.     Synergism is also called synergy.

Synthetic Detergent

A manufactured cleaning agent.     Detergents can be classified as anionic, cationic, or nonionic.

Synthetic Organic Chemicals

Man-made organic substances including herbicides, pesticides, and various industrial chemicals and solvents.     Synthetic organic chemicals are generally considered dangerous in drinking water at concentrations above the USEPA maximum contaminant levels.     Often referred to as SOCs.


A complete integrated series consisting of various components and perhaps multiple water treatment processes which can be tested, installed, and operated as a singular unit of equipment.     For example, a single RO treatment system generally consists of two or more stages of media filtration plus cross flow membrane filtration and water storage.

System with a Single Service Connection

A public water system which supplies drinking water to consumers via a single service line.


Relating to whole body, rather than its individual parts.

Systemic Effects

Effects observed at sites distant from the entry point of a chemical due to its absorption and distribution into the body.

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Updated on Mon, 22 Jun 2020 by Jonathan

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