SDWA requires states to report drinking water information periodically to EPA; this information is maintained in the federal database, SDWIS/Fed. SDWIS stands for the Safe Drinking Water Information System and contains information submitted by public water systems to primacy agencies, and by primacy agencies to EPA, to meet the reporting requirements established by the Safe Drinking Water Act (SDWA) and related regulations and guidance.

Data Completeness: EPA is aware of inaccuracies and underreporting of some violation data to SDWIS. Due to the known incompleteness of the data reported by states and regions, we refer to systems as having reported violations or no reported violations.

Frequency of Data Updates: Reported violations may be between 3 and 6 months old by the time they appear in the dashboard, because they are reported to EPA in the fiscal year quarter following the quarter in which they occur. For example, data about enforcement actions taken by September 30 in a given year will become final in SDWIS on December 31, and become available in the dashboard in January or later.

Sample Values: Sample contaminant values that trigger Maximum Contaminant Level (MCL) or Maximum Residual Disinfectant Level (MRDL) violations are not always available in EPA's database of record (SDWIS/Fed). States collect detailed sampling data from public water systems, and are required to submit a portion of their data to EPA. All violations are required to be reported to EPA, but only a subset of the measured values and units are required to be reported to EPA. To find out more about the available sample data, contact your state drinking water program or local water system.

A public water system (PWS) is a system for the provision to the public of water for human consumption through pipes or other constructed conveyances, if such system has at least 15 service connections or regularly serves at least 25 individuals at least 60 days out of the year.

Public water systems can be categorized by type:

• Community Water System - A PWS that serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents (e.g., homes, apartments and condominiums that are occupied year-round as primary residences).
• Non-transient Non-community Water System - A non-community PWS that regularly serves at least 25 of the same persons over six months per year. A typical example of a non-transient non-community water system is a school or an office building that has its own water source, such as a drinking water well.
• Transient Non-community Water System - A non-community PWS that does not regularly serve at least 25 of the same persons over six months per year. A typical example is a campground or a highway rest stop that has its own water source, such as a drinking water well.

Public water systems can also be categorized by size, based on the number of people served by the system:

• Very Small water systems serve 25-500 people
• Small water systems serve 501-3,300 people
• Medium water systems serve 3,301-10,000 people
• Large water systems serve 10,001-100,000 people
• Very Large water systems serve 100,001+ people.

Violations required to be reported under SDWA are grouped into the following categories:

• Health-Based - These violations fall into three categories: 1) exceedances of the maximum contaminant levels (MCLs), which specify the highest allowable contaminant concentrations in drinking water, 2) exceedances of the maximum residual disinfectant levels (MRDLs), which specify the highest concentrations of disinfectants allowed in drinking water, and 3) treatment technique requirements, which specify certain processes intended to reduce the level of a contaminant. Acute health-based violations are those that may cause illness after a short-term exposure.
• Monitoring and Reporting - Failure to conduct regular monitoring of drinking water quality, or to submit monitoring results in a timely fashion to the state primacy agency or EPA, as required by SDWA.
• Other Violations - Violations of variances and exemptions, public notice and Consumer Confidence Rule requirements, and others not referenced above.

Eligible states, territories, and tribes develop and implement a Public Water System Supervision (PWSS) program adequate to enforce the requirements of the SDWA and ensure that water systems comply with the National Primary Drinking Water Regulations. EPA works with these primacy agencies to ensure that they carry out key activities essential to SDWA Public Water Systems Supervision program.

Currently, all states and territories except Wyoming and the District of Columbia have primacy for the PWSS program. The Navajo Nation is the only Indian tribe to have sought and received primacy for the PWSS program. EPA has primacy in Wyoming and the District of Columbia, and in Indian country, excluding the Navajo Nation, and retains enforcement authority in primacy states.

Key activities carried out by primacy agencies include: 

• developing and maintaining state drinking water regulations that are at least as protective as EPA’s,
• developing and maintaining an inventory of public water systems throughout the state,
• developing and maintaining a database to hold compliance information on public water systems,
• conducting sanitary surveys of public water systems,
• reviewing public water system plans and specifications,
• providing technical assistance to managers and operators of public water systems,
• carrying out a program to ensure that the public water systems regularly inform their consumers about the quality of the water that they are providing,
• certifying laboratories that can perform the analysis of drinking water that will be used to determine compliance with the regulations, and
• carrying out an enforcement program to ensure that the public water systems comply with all of the state's requirements.

Generally, a primacy agency's first responses to violations are informal actions such as reminder letters, warning letters, notices of violation, field visits, and telephone calls.

If a violation continues or recurs, the primacy agency must initiate a formal enforcement response that requires the violating public water system to return to compliance on an enforceable schedule. Formal enforcement responses include citations, administrative orders with or without penalties, civil referrals to state attorneys general or to the U.S. Department of Justice, filing criminal charges, and other sanctions.

If there is risk to public health, EPA and the primacy agency can issue emergency orders that require the public water system to take immediate action to protect public health and return the system to compliance.

EPA assigns either one, five, or ten points to each uncorrected violation as a reflection of the violation's severity. All violation points are summed and a score assigned to each PWS. Systems called "serious violators" have an aggregate score of at least eleven points. EPA’s Enforcement Response Policy directs primacy agencies to ensure that serious violators return all uncorrected violations to full compliance within six months of becoming a serious violator, or be placed under formal enforcement to compel the serious violator to take action to return to compliance.