A facility with a secondary treatment water system is one that receives potable water from a public water supply and adds chemicals to provide additional treatment to their drinking water. Addition of chemicals can be done by injection or by other means such as Copper-Silver Ionization. Treated water is then delivered to consumers through the facility premise plumbing. Often, these facilities are using chemical disinfectants to reduce the risk of opportunistic pathogens such as Legionella from occurring within premise plumbing. Other facilities add chemicals for corrosion control to reduce exposure to lead, copper, and other metals that may leach from premise plumbing and water fixtures. Such water systems are considered treatment facilities, and as such, are subject to regulations as public water supplies under the Michigan Safe Drinking Water Act (Act 399). These water systems will be classified and regulated as either community water supplies or noncommunity water supplies. Facilities planning to install treatment as described here must submit the following three applications before installation:

• Application for Secondary Treatment Public Water Supply Designation
• Secondary Treatment Nontransient Noncommunity Water Supply Capacity Development Plan
• Permit Application to Install or Alter Secondary Treatment

As a regulated Public Water Supply, the facility must contract a certified operator to manage the system and submit monthly operation reports and laboratory results as required by the Safe Drinking Water Rules.