Updated
A city between two rivers that mostly drinks one
The St. Louis Water Division has supplied the city since 1835. Its two plants produced an average of 125 million gallons a day in 2025. Both plants won the Partnership for Safe Water's Phase III 20-Year Directors Award for treatment.
Where the intakes are
Howard Bend, in west St. Louis County, draws from the Missouri River. Chain of Rocks sits on the Mississippi just below the point where the Missouri joins it. Rivers run side by side for miles before they mix, though, so Chain of Rocks also takes in mostly Missouri water. That's why both plants deal with the same thing: a muddy, mineral-rich river that drains farmland across the Great Plains. The state completed a source water assessment of that susceptibility in 2004.
Softening and pH
Both plants use precipitative softening along with sedimentation, flocculation, filtration and chlorine. Softening removes much of the river's hardness and gives the water a high pH:
| Parameter (2025) | Average | Range |
|---|---|---|
| Total hardness | 129 ppm (7.5 gpg) | 80–206 |
| Non-carbonate hardness | 74 ppm | 38–155 |
| pH | 9.52 | 8.52–10.05 |
| Sodium | 45.4 ppm | 26.8–62.5 |
| Sulfate | 131 ppm | 87.6–176.5 |
| Dissolved solids | 298 ppm | 216–388 |
Because the hardness swings with the river, a softener sized for the average can fall short in the hardest months. Run the softener sizing calculator at the 206 ppm high (about 12 gpg) instead. The fairly high sulfate also gives the water a slight mineral taste.
Farm chemicals and PFAS
- Atrazine: up to 0.96 ppb, a clear sign of upstream row-crop runoff, but under the 3 ppb limit
- Nitrate: 0.58 ppm (limit 10)
- Arsenic: 0.42 ppb
- PFAS: all 29 compounds in the 2024 UCMR 5 round were below minimum reporting levels
- Byproducts: distribution-site running averages of 7.8–11.7 ppb TTHM and up to 15.4 ppb HAA5, low for a river system
- Coliform: 0.0% positive for the year
Lead
St. Louis has a lot of old brick housing, and the report states plainly that elevated lead was found in some homes. In June–September 2025 reduced monitoring, 50 taps were sampled. The 90th percentile was 1.80 ppb, the range was non-detect to 6.87 ppb, and no samples exceeded the action level. Copper's 90th percentile was 0.0238 ppm. The Water Division says its corrosion treatment is optimized, but individual service lines still matter. Look up your address in the inventory. Until you know what your line is made of, a lead-certified filter is cheap insurance. The filter selector explains which certifications to look for, and the filter vs. bottled water calculator shows why bottled water is the expensive option.
St. Louis residents ask
Does St. Louis drink Mississippi River water?
Mostly not. The Chain of Rocks plant sits on the Mississippi just south of the confluence, but the report says the two rivers haven't fully mixed at its intake, so the water there is mostly from the Missouri. The Howard Bend plant draws straight from the Missouri River.
What was the reporting violation?
The city didn't certify to the state, on time, that it had sent the required notices to customers served by lead, galvanized-requiring-replacement or unknown service lines. The violation concerns paperwork and notification, not a water quality limit.
How do I find out what my service line is made of?
Check the Water Division's lead service line inventory at stlwater.com/water-quality/lead-and-water.php or call (314) 771-2255. If a line might contain lead, the report suggests flushing the cold tap for 5 minutes before drinking or cooking.
Why is St. Louis water so alkaline?
The plants use precipitative (lime) softening, which raises pH. The 2025 distribution average was 9.52, with a range of 8.52–10.05.
Documents used
- City of St. Louis Water Division, 2025 Water Quality Report
- St. Louis Water Division: lead and water
- Missouri source water assessments (University of Missouri / DNR)
Reviewed November 1, 2026 against the sources above. Public water system ID MO6010715 (City of St. Louis Water Division). Figures describe the utility's system, not your home's plumbing; a certified lab test tells you what comes out of your tap. Spot an error? Tell us.