Section R. 325.10611a - Filtration and disinfection; disinfectionRule 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.Mich. Admin. Code R. 325.10611a