EPA developed the NCOD to satisfy the statutory requirements set by Congress in the 1996 amendments to the Safe Drinking Water Act (SDWA) to maintain a national drinking water contaminant occurrence database using samples data for both regulated and unregulated contaminants in public water systems.
This site describes water sample analytical data that EPA is currently using and has used in the past for analysis, rulemaking, and rule evaluation. The data have been checked for data quality and analyzed for national representativeness.
Click here for more information and to read data links.
Source: EPA.gov