The St. Louis water system consists of approximately 35 miles of water main ranging in size from 4 inch to 16 inch. In the Fall of 2015, the City switched from providing water to its customers from municipal wells to treated water provided by the Gratiot Area Water Authority (GAWA). GAWA consists of the Cities of Alma and St. Louis and provides treated water to both communities from its water treatment plant located in the City of Alma. Water is supplied to GAWA via six groundwater wells (three recently constructed with funds provided by the City of St. Louis and the USEPA) and the Pine River in Alma. An additional well is expected to be constructed to provide the well capacity St. Louis had in its own municipal well system.

The Federally mandated Consumer Confidence Report (CCR) has been published annually since 1998. This testing is performed at the GAWA water treatment plant, the GAWA well fields, Pine River intake, the Alma distribution system and the St. Louis water distribution system regularly. The testing has shown that the water being supplied to our customers is safe and well within the State and Federal guidelines. Consumer Confidence Reports are available to all water customers. The reports can be downloaded below. Copies are also available upon request at City Hall.

Water system pressure is maintained by two elevated water storage towers located within the City. The 500,000-gallon facility was upgraded and painted in 2018 while the 250,000-gallon facility was constructed and put into service in 2016. These two towers allow the City to maintain a system pressure of between 55-65 psi. Fire service is provided from over 260 fire hydrants. In 2020 the City purchased 259 million gallons of water from GAWA, for an average daily water flow of 709,589 gallons.