Definition: Number of water quality violations for public water systems, by type of violation (e.g., in 2015, 1,533 Maximum Contaminant Level (MCL) violations were issued in California). MCL violations occur when contaminant levels in drinking water supplies exceed limits set by the California Dept. of Public Health. Monitoring and reporting violations occur when a public water system fails to have its water tested as required or fails to report test results correctly.