Water Quality Terms

90th percentile - 90 percent of the analytical results in the sample data set are equal to or lower than the analytical result listed.

AL (action level) - The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.

BDL - below detection level

HBRV – health based reference value

LRAA (locational running annual average) – The average of sample analytical results for samples taken at a particular monitoring location during the previous four quarters.

MCL (maximum contaminant level) - The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the maximum contaminant level goals (MCLGs) as feasible using the best available treatment technology.

MCLG (maximum contaminant level goal) - The level of a contaminant in drinking water below which there is no known or expected risk to human health. MCLGs allow for a margin of safety.

MRDL (maximum residual disinfectant level) - The highest level of the disinfectant allowed in drinking water. There is convincing evidence that the addition of disinfectant is necessary for control of microbial contaminants.

N/A - not applicable

ND - non-detect

NTU (nephelometric turbidity units) - Unit to measure turbidity.

org/10L - organisms per 10 liters

PFAS (per- and polyfluoroalkyl substances) – A group of manufactured chemicals that have been used in industry and consumer products since the 1940s.

ppm - parts per million (also known as milligrams per liter [mg/L])

ppb - parts per billion (also known as micrograms per liter)

ppt – parts per trillion (also known as nanograms per liter)

pCi/L (picocuries per liter) - Used to measure radioactivity.

RAA (running annual average) - The average of sample analytical results for samples taken during the previous four quarters.

SMCL (secondary maximum contaminant limits) - Non-mandatory guidelines established by the U.S. EPA to assist utilities in managing drinking water for aesthetic considerations, such as taste, odor, and color. These contaminants are not considered to present a risk to human health at the SMCL.

TOC - total organic carbon

TT (treatment technique) - A required process intended to reduce the level of a contaminant in drinking water.

Turbidity - The measure of the cloudiness of water. Citizens monitors turbidity as an indicator of the effectiveness of the filtration system.