R 325.10611a Filtration and disinfection; disinfection.

Rule 611a. (1) Subpart H supplies shall provide sufficient disinfectant contact time before the water enters the distribution system to assure adequate disinfection. (2) Subpart H supplies shall provide disinfection treatment achieving all of the following conditions: (a) The disinfection treatment shall be sufficient to ensure that the total treatment processes of that system achieve the standards set forth in R 325.10611(3)(a). (b) The residual disinfectant concentration in the water entering the distribution system shall not be less than 0.2 milligrams per liter for more than 4 hours. (c) The residual disinfectant concentration in the distribution system, measured as total chlorine, free available chlorine, combined chlorine, or chlorine dioxide shall not be undetectable in more than 5% of the samples each month for any 2 consecutive months that the supply serves water to the public. Water in the distribution system that has a heterotrophic bacteria concentration less than or equal to 500 per milliliter, measured as heterotrophic plate count (HPC), is considered to have a detectable disinfectant residual for purposes of determining compliance with this subdivision. (d) If the department determines, based on site specific considerations, that a supply does not have means for having a sample transported and analyzed for HPC and that the supply is providing adequate disinfection in the distribution system, then the requirements of subdivision (c) of this subrule do not apply.