Frequent Questions

What must a public water system using chlorine or chloramines measure to determine compliance with the maximum residual disinfectant level (MRDL)?

For compliance with the Stage 1 Disinfectants and Disinfection Byproducts Rule, community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) using chlorine to maintain a residual disinfectant must measure either free chlorine or total chlorine to determine compliance with the MRDL. CWSs and NTNCWs using chloramines to maintain a residual disinfect must measure either total chlorine or combined chlorine (63 FR 69390, 69425; December 16, 1998).
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