Miami tap water comes primarily from the Biscayne Aquifer, a shallow porous-rock formation just below the South Florida land surface that fills as rainwater seeps through it, according to WASD's 2025 report. Many residents in the area receive water through the Miami-Dade Water and Sewer Department, though your last water bill will show which utility serves you. WASD's report covers monitoring from January 1, 2025 to December 31, 2025, and describes water reaching homes through three main treatment plants. The Alexander Orr Jr. plant uses lime treatment to reduce hardness, then disinfects and filters. The Hialeah Water Treatment Plant uses lime softening, disinfection, and filtration, plus air stripping to remove volatile organic builds up. After treatment, WASD adds chlorine as a primary disinfectant, then adds ammonia to combine with the chlorine and form chloramine, which serves as the secondary disinfectant to protect water in the distribution system, according to WASD's 2025 report.
WASD's 2025 report does not include a hardness figure for the main system. If that question matters to you, the guide on hard water in Miami is a good next read. For help reading what WASD does publish, see how to read your utility's annual water report.