Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water.† Primary MCLs are set as close to the PHGs (or MCLGs) as is economically and technologically feasible.† Secondary MCLs are set to protect the odor, taste, and appearance of drinking water.
Primary Drinking Water Standards (PDWS): MCLs for contaminants that affect health along with their monitoring and reporting requirements, and water treatment requirements.
Secondary Drinking Water Standards (SDWS):† MCLs for contaminants that affect taste, odor, or appearance of the drinking water.† Contaminants with SDWSs do not affect the health at the MCL levels.
ND: not detectable at testing limit†
ppm: parts per million or milligrams per liter (mg/L)
ppb: parts per billion or micrograms per liter (ug/L)
ppt: parts per trillion or nanograms per liter (ng/L)
pCi/L: picocuries per liter (a measure of radiation)
Public Health Goal (PHG): The level of a contaminant in drinking water below which there is no known or expected risk to health.† PHGs are set by the California Environmental Protection Agency.
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 are set by the U.S. Environmental Protection Agency (USEPA).
Maximum Residual Disinfectant Level (MRDL):† The level of a disinfectant added for water treatment that may not be exceeded at the consumerís tap.
Maximum Residual Disinfectant Level Goal (MRDLG): The level of a disinfectant added for water treatment below which there is no known or expected risk to health.† MRDLGs are set by the U.S. Environmental Protection Agency.
Treatment Technique (TT):† A required process intended to reduce the level of a contaminant in drinking water
Regulatory Action Level (AL): The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.
Variances and Exemptions:† Department permission to exceed an MCL or not comply with a treatment technique under certain conditions.
The sources of drinking water (both tap water and bottled water) include rivers, lakes, streams, ponds, reservoirs, springs, and wells.† As water travels over the surface of the land or through the ground, it dissolves naturally-occurring minerals and, in some cases, radioactive material, and can pick up substances resulting from the presence of animals or from human activity.
Contaminants that may be present in source water include:
∑ Microbial contaminants, such as viruses and bacteria, that may come from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife.
∑ Inorganic contaminants<