2024 Official Test Results — Key Findings

• Overall Compliance: St. Louis’s 2024 Consumer Confidence Report, published March 2025, confirms the city met or exceeded all state and federal drinking water standards. The Water Division has never exceeded a Maximum Contaminant Level for any regulated contaminant in its 120-year testing history.
• PFAS — Zero Detected: In 2024, the Water Division participated in UCMR 5 monitoring, testing for all 29 PFAS compounds plus lithium. All 29 PFAS contaminants were below their minimum reporting level — a clean result, and an important reassurance for St. Louis residents given the national PFAS picture. Lithium was detected at an average of 27.5 ppb (range 15.4–45.3 ppb) from natural mineral sources — an unregulated contaminant being studied nationally.
• Detected Inorganics (2024 — all within MCLs): Arsenic 0.39 ppb (MCL 10 ppb); chromium total 0.93 ppb (MCL 100 ppb); nitrate+nitrite 2.099 ppm (MCL 10 ppm); barium 0.027 ppm (MCL 2 ppm); nickel 0.85 ppb; selenium 1.18 ppb; antimony 0.31 ppb. Atrazine was detected at 0.57 ppb (MCL 3 ppb), from herbicide runoff upstream.
• Fluoride: Detected at up to 0.76 ppm in 2024, within the Water Division’s target of 0.6 ppm and well below the 4 ppm MCL. Fluoridation has been in place since 1953.
• Microbiology: No Cryptosporidium or Giardia detected in finished water. The multi-stage treatment process — precipitative softening, sedimentation, flocculation, filtration, and chlorine disinfection — effectively removes microbial threats from the river source water.

Lead Service Lines — The Priority Concern for 2026

• Scale of the Issue: City of St. Louis records indicate approximately 113,000 service lines in total — around 9,000 classified as lead, 46,000 confirmed non-lead, and 58,000 of unknown material still requiring survey. St. Louis ranks 7th among major US cities for the number of lead service lines according to NRDC analysis.
• 2022 Lead and Copper Results (most recent programme data): The 90th percentile lead result in the first half of 2022 was 0.89 ppb; in the second half of 2022 it was 2.12 ppb — both below the 15 ppb action level. However, one sample in the first half of 2022 exceeded the action level at 49.2 ppb, highlighting the risk in homes with active lead plumbing. No copper samples exceeded the 1,300 µg/L action level.
• Inventory and Replacement Programme: In November 2024 the Water Division contacted all property owners with lead, galvanised-requiring-replacement, or unknown service lines, as required under the EPA’s revised Lead and Copper Rule (October 2024). The City has applied for $5 million in federal Bipartisan Infrastructure Law funding through Missouri DNR’s FY2025 Drinking Water State Revolving Fund — now on the fundable list. A zero-interest loan programme for voluntary replacement is also being developed.
• Corrosion Control: The Water Division has operated an optimised corrosion control treatment strategy for over 20 years, minimising lead leaching from service lines and internal plumbing into the distribution system. This keeps system-wide 90th percentile results well below the action level, though individual homes with lead lines at the tap can still see elevated readings.
• What You Can Do: If your home was built before 1986, or your property received a letter from the Water Division, flush your cold tap for at least 5 minutes before using water for drinking or cooking, especially after periods of non-use. A lead-certified filter (NSF/ANSI Standard 53 or 58) provides the most reliable ongoing protection.

Mississippi & Missouri River Sources

• Dual River System: The Howard Bend Plant draws from the Missouri River; the Chain of Rocks Plant sits on the Mississippi south of the confluence. In practice, both intakes receive primarily Missouri River water. Continuous real-time monitoring tracks source water turbidity, temperature, pH, and contaminants at intake.
• Agricultural Runoff: The Missouri DNR source water assessment identifies the river sources as susceptible to contamination given the vast multi-state upstream watershed. Atrazine (herbicide), nitrate (fertiliser), and sediment are the primary agricultural concerns. Detected levels in 2024 were well within MCLs.
• Seasonal Variation: River water quality fluctuates significantly with temperature, rainfall, and upstream activity. High-organic-content periods (typically spring and autumn) increase disinfection byproduct formation. Cloudy water in winter is caused by dissolved oxygen released as temperature rises — safe to drink, not a sign of contamination.

Treatment and Infrastructure

• Multi-Stage Treatment: Both plants use precipitative softening, coagulation, flocculation, sedimentation, filtration, and chlorine disinfection. The Water Division is a charter member of the EPA/AWWA Partnership for Safe Water, and received the Phase III 20-Year Directors Award for both treatment plants — a mark of sustained operational excellence.
• Disinfection Byproducts: Chlorine treatment of high-organic river water generates trihalomethanes (TTHMs) and haloacetic acids (HAAs) in the distribution system — particularly at the system’s extremities. All values remain within federal MCLs. EWG’s independent health guidelines (based on peer-reviewed cancer risk studies) set far lower benchmarks than federal MCLs, and flag these as a concern for long-term exposure. A carbon block or reverse osmosis filter at the tap significantly reduces DBP exposure.
• Infrastructure Investment: The Water Division continues annual water main replacement to address ageing infrastructure. Advanced SCADA monitoring and pressure management systems enable rapid response to breaks and quality events across the 1,300+ mile distribution network. See our national water quality tool to see how St. Louis compares with other cities.