Key Water Quality Terms

• Water System - A public water system provides water for human consumption through pipes or other constructed conveyances to at least 15 service connections or serves an average of at least 25 people for at least 60 days a year. A public water system may be publicly or privately owned.

• Water District - A water district is a local corporate entity that operates and maintains a water supply system in one or more provincial cities or municipalities.

• Groundwater - Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water.

• Surface water - Surface water is water located on top of the Earth's surface such as rivers, creeks, and wetlands. This may also be referred to as blue water. The vast majority is produced by precipitation and water runoff from nearby areas.

• Well water - A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers.

• Domestic well - Domestic well means a well primarily used for potable non-public water supply purposes and which may be used for non-potable purposes, excluding heat pump supply.

• Municipal water - A public water supply system or water supply network including water treatment facilities, water storage facilities (reservoirs, water tanks and water towers) and a pipe network for distributing the treated water to customers including residential, industrial, commercial or institutional establishments.

• Irrigation well - Also referred to as an agricultural well or stock well, means any well used solely to supply water for irrigation or other agricultural purposes. 

• Water system types (EPA) 

  • Community Water System (CWS). A public water system that supplies water to the same population year-round.

  • Non-Transient Non-Community Water System (NTNCWS). A public water system that regularly supplies water to at least 25 of the same people at least six months per year. Some examples are schools, factories, office buildings, and hospitals which have their own water systems.

  • Transient Non-Community Water System (TNCWS). A public water system that provides water in a place such as a gas station or campground where people do not remain for long periods of time.

Understanding Contaminants

There are a variety of contaminants within drinking water that are constantly measured and regulated within water districts and systems. The EPA sets health guidelines for the maximum contaminant level of many chemical, biological, physical and radioactive contaminants that threaten public health when in large quantities. The following list highlights key terms when discussing water quality and measuring contamination according to the EPA. 

• 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.

• 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 (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 Residual Disinfectant Level Goal (MRDLG) - The level of a 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.

• Treatment Technique (TT) - A required process intended to reduce the level of a contaminant in drinking water.

• Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

• 2 Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million (PPM).

• Exceeding Compliance - if a contaminant's values exceeds the state and EPA guidelines, then the associated water system is exceeding compliance and must take action to mitigate the issue and bring the water quality back into the regulation limits.