Frequent Questions

What are the requirements for public water systems (PWSs), including PWSs that only purchase water, storing finished water in uncovered storage facilities?

PWSs subject to Subpart P of Part 141 are not permitted to construct uncovered finished water storage facilities as of February 16, 1999 (40 CFR 141.170(c)). PWSs subject to Subpart T must cover finished water reservoirs (storage facilities) constructed on or after March 15, 2002 (40 CFR 141.511). PWSs (Subpart H systems) with existing uncovered finished water storage must notify the state of use of uncovered finished water storage facilities. PWSs must cover all uncovered finished water storage facilities or treat discharge from the finished water storage facilities to the distribution system to an inactivation/removal of 4-log virus, 3-log Giardia lamblia, and 2-log Cryptosporidium. Alternatively, a PWS must be in compliance with a state-approved schedule (40 CFR 141.714).

The National Primary Drinking Water Regulations are available at

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