What is the required minimum residual disinfectant level for chlorine in water supplied by public water systems (PWSs)?
For PWSs that use surface water or ground water under the influence of surface water (Subpart H systems) the residual disinfectant concentration in the water entering the distribution system cannot be less than 0.2 mg/L for more than 4 hours [40 CFR 141.72(a)(3) & (b)(2)]. The residual disinfectant concentration in the distribution system cannot be undetectable in more than 5% of the samples each month, for any 2 consecutive months that the system serves water to the public [40 CFR 141.72(a)(4) & (b)(3)].
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