There are many causes and sources for taste and odor problems. The chemicals responsible for these problems in drinking water are mostly considered to contribute undesirable aesthetic effects, such as bad tastes, odors and off color or cloudiness. These contaminants and those covered under the USEPA National Secondary Drinking Water Regulations (NSDWRs) at the Secondary Maximum Contaminant Level (SMCL) are not considered to be a health concern. Most of these contaminants fall under the NSDWRs which set non-mandatory water quality standards (SMCLs) for 15 contaminants. However, some of the above listed chemicals do fall under the National Primary Drinking Water Regulations (NPDWRs), such as chlorine disinfectants, copper, some of the petroleum products and chlorinated organics. The USEPA recommends secondary standards to water systems but does not require systems to comply. However, states may choose to adopt the NSDWRs as enforceable standards. Chlorine residuals are the most common odor problem in North American drinking waters. This is because standard chlorination procedures are required by regulatory requirements to provide a measurable level of chlorine residual as free chlorine or chloramine at the taps of water consumers. This results in a chlorinous or bleach-like smell or flavor. The average person can smell/taste free chlorine (Cl2, HOCl, OCl- – at 0.5 – 1 mg/L) more so than monochloramine (NH2Cl – at 3 mg/L). Odor detection and measurement of organic-based odorants are rather subjective and can be very expensive if analytical instrumentation is utilized to accurately identify and quantify the odorproducing substance. Most public utilities utilize sensory panels to detect and determine a ‘threshold odor number’ (TON) or establish a category for the description of the contaminant in accordance with procedures in Standard Methods for the Examination of Water and Waste Water – 2170 Flavor Profile Analysis.
