Radium in Drinking Water

Radium is formed when uranium and thorium undergo radioactive decay in the environment. Two of the main radium isotopes found in the environment are radium-226 and radium-228. Radium emits energy in the form of alpha particles and gamma rays, and will also decay to form radon. Radium in drinking water is of primary concern because this radiation may cause cancer, kidney damage and birth defects. Additionally, the decay of radium into radon presents another contaminant of health concern in drinking water as well as in the air.

Contaminant  In Water As Maximum Contaminant Level


Radium (Ra)



US EPA (Radium 226 and 228 combined):
MCL* = 5.0 pCi/L
MCLG** = zero pCi/L

WHO† Guideline:
Radium 226 = 1 Bq/l
Radium 228 = 0.1 Bq/l

Health Canada (Radium 226 only):

MAC*** = 0.5 Bq/L (13.5 pCi/L)

Sources of Contaminant

Radioactive decay of uranium and thorium in rocks and soil

Potential Health Effects

Increased risk of cancer

Treatment Methods Cation Exchange Softening
Reverse Osmosis
Lime Softening

*Maximum Contaminant Level (MCL) — The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.

**Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.

***Maximum Acceptable Concentration (MAC) - established for parameters which when present above a certain concentration, have known or suspected adverse health effects.

WHO† - World Health Organization

Click here to open WQA's Technical Fact Sheet on Radium.

Click here to access all of WQA's Technical Fact Sheets.