Tracking Community Water
The drinking water data used in the Tracking Network are gathered as part of the water quality monitoring requirements set out by the U.S. Environmental Protection Agency (EPA) and state agencies. Tracking Network data are the only set of consistent drinking water quality data nationwide. While they are not gathered specifically to assess the level of exposure or to track changes in water quality over time, they can be used to determine the potential for public health impacts from contaminant levels of concern.
The main issues considered in the development of the contaminant-specific measures presented on the Tracking Network included the following.
Exposure patterns. The measures of concentration were chosen for each contaminant on the Tracking Network based on the type of exposure and the common health effects.
Monitoring requirements / sampling frequency. Each of the contaminants on the Tracking Network has different sampling requirements in terms of frequency and location of sampling. Monitoring requirements are based on the potential for contamination. It is important to understand the monitoring requirements when interpreting the summary measures presented on the Tracking Network.
EPA requires community water systems to provide drinking water that meets standards established under the Safe Drinking Water Act. EPA
- establishes drinking water standards for individual contaminants and groups of contaminants, typically Maximum Contaminant Levels (MCL) -- When a contaminant in drinking water cannot be measured feasibly, EPA establishes drinking water Treatment Technique Requirements (TTR) based on indicators of water quality
- sets up requirements for making sure water systems follow the regulations, and
- sets requirements about the treatment required and ways to measure how well the treatment processes work.
Censored values. Censored values refer to contaminant concentrations that cannot be detected with standard lab tests or are below a certain reporting level. Censoring of sample concentration results varies by laboratory methods and by contaminant. Censoring can range from 10-90%. Methods for handling censored values were carefully considered and defined for each measure.
Reference or benchmark levels. Several measures on the Tracking Network use comparisons to commonly-used benchmarks, such as the Maximum Contaminant Level (MCL). MCLs are developed to account for possible health risks, as well as how practical it is to treat water so that the contaminant concentration is lowered. However, the public health significance of reference levels varies by contaminant.
Drinking water standards and monitoring requirements change often. EPA may add contaminants to the list of those currently regulated. Also, EPA periodically must review and, if necessary, revise existing regulations. Revisions are made when new information is available about health effects, treatment, analytical methods, and contaminant occurrence.