Glossary
The terms on this site are EPA's own. These are their definitions in plain language.
System types
Community water system. Serves the same people year-round: a city, town, subdivision, or mobile home park. This is the type that serves homes.
Non-transient non-community system. Serves the same people for at least six months a year but not where they live: a school, factory, or office with its own water supply.
Transient non-community system. Serves people who pass through: a campground, rest stop, or restaurant with its own well.
Water sources
Ground water. Wells and springs. Surface water. Rivers, lakes, and reservoirs. Ground water under the direct influence of surface water. Wells close enough to surface water that they must be treated as surface water. Purchased. Water bought from another system.
Compliance and violations
Violation. A failure to meet a requirement of a drinking water rule. It can be an exceedance of a contaminant limit, a missed treatment step, or a failure to test, report, or notify customers on time. Most violations are of the last kind.
Health-based violation. An exceedance of a maximum contaminant level or maximum residual disinfectant level, or a treatment technique violation.
Health flag. EPA's indicator that a system has at least one open health-based violation.
Serious violator. EPA's designation, also called an enforcement priority, for a system with unresolved serious, multiple, or continuing violations.
Unresolved violation. A violation that was still open at the time the data was retrieved.
Quarterly compliance history. EPA's record of a system's status in each of the last twelve completed quarters, plus the quarter in progress at the last data refresh.
Sanitary survey. An on-site review of a system's sources, treatment, storage, and operations by the state, normally every three to five years.
Lead and copper
Action level. Lead and copper have no maximum contaminant level. If more than 10 percent of tap samples exceed 15 parts per billion of lead or 1.3 milligrams per litre of copper, the system must take corrective action. Action level exceedance. A sampling round in which that threshold was passed.
Limits
Maximum contaminant level (MCL). The highest level of a contaminant allowed in drinking water. Maximum residual disinfectant level (MRDL). The highest level of a disinfectant such as chlorine allowed. Treatment technique. A required process, used where measuring a contaminant directly is impractical.