KEY TERMS AND ABBREVIATIONS

Term	Definition
µS/cm	Microsiemens per centimeter; measure of electrical conductivity.
90th Percentile	The value for which 90 percent of samples had a lower result.
AL	Action Level: The concentration of a contaminant which, if exceeded, triggers treatment or other requirements that a water system must follow.
constituent	A chemical or parameter measured in the water supply.
DBP	Disinfection By-Products: Substances that can form during a reaction of a disinfectant with naturally present organic matter in the water.
MCL	Maximum Contaminant Level: The highest level of a contaminant that is allowed in drinking water. Primary MCLs are set as close to the PHG (or MCLGs) as is economically and technologically feasible. Secondary MCLs are set to protect the odor, taste, and appearance of drinking water.
MCLG	Maximum Contaminant Level Goal: 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.
MRDL	Maximum Residual Disinfectant Level: The highest level of a disinfectant allowed in drinking water. There is convincing evidence that the addition of a disinfectant is necessary for control of microbial contaminants.
MRDLG	Maximum Residual Disinfectant Level Goal: The level of drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.
NA	Not Applicable.
ND	Not Detected.
NTU	Nephelometric Turbidity Units; measures cloudiness of water.
oocysts/L	oocysts per liter; count of organisms.
pCi/L	Picocuries per liter; measures radiation.
PHG	Public Health Goal: 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.
ppb	parts per billion; one ppb is like 3 seconds in 100 years.
ppm	parts per million; one ppm is like 32 seconds in one year.
ppt	parts per trillion; one ppt is like 3 seconds in 100,000 years.
TOC	Total Organic Carbon; a measurement of the potential of water to form DBPs.
TT	Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.