Contaminants and rules in Missouri water systems
78 different rules and contaminants appear in the past three years of violation records for Missouri's 2,835 active public water systems. The tables show how many systems each one affected and how many of those violations are still unresolved. Most entries are monitoring, reporting, or notification lapses rather than confirmed contamination.
Microbial
Bacteria and the rules that test for them. Health-based when a sample is positive.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Revised Total Coliform Rule (RTCR) | 8000 | 858 | 30% | 228 |
| E. coli (Escherichia coli) | 3014 | 53 | 2% | 51 |
Inorganic Chemical
Naturally occurring or from fertilizer and industry. Each has a maximum contaminant level.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Nitrate-Nitrite (Combined) | 1038 | 159 | 6% | 1 |
| Fluoride | 1025 | 25 | 1% | 4 |
| Cadmium | 1015 | 22 | 1% | 2 |
| Arsenic | 1005 | 21 | 1% | 2 |
| Barium | 1010 | 21 | 1% | 2 |
| Chromium | 1020 | 21 | 1% | 2 |
| Mercury | 1035 | 21 | 1% | 2 |
| Selenium | 1045 | 21 | 1% | 2 |
| Antimony | 1074 | 21 | 1% | 2 |
| Beryllium | 1075 | 21 | 1% | 2 |
| Thallium | 1085 | 21 | 1% | 2 |
| Cyanide | 1024 | 11 | 0% | 1 |
Disinfection Byproduct
Formed when chlorine reacts with organic matter in the water.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| TTHM (Total Trihalomethanes) | 2950 | 107 | 4% | 18 |
| Total Haloacetic Acids (HAA5) | 2456 | 98 | 3% | 10 |
| Stage 1 Disinfectants and DBP Rule | 0400 | 4 | 0% | 4 |
| Chlorite | 1009 | 3 | 0% | 0 |
| Stage 2 Disinfectants and Disinfection Byproducts Rule | 0600 | 1 | 0% | 1 |
Treatment Technique
Rules that require a process, such as corrosion control or disinfection, rather than a measured limit.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Lead and Copper Rule Revisions (LCRR) | 5200 | 285 | 10% | 285 |
| Lead and Copper Rule (LCR) | 5000 | 196 | 7% | 196 |
| Groundwater Rule (GWR) | 0700 | 140 | 5% | 59 |
| Interim Enhanced Surface Water Treatment Rule | 0300 | 24 | 1% | 3 |
| Surface Water Treatment Rule (SWTR) | 0200 | 21 | 1% | 0 |
| Long Term 2 Enhanced Surface Water Treatment Rule (LT2) | 0800 | 3 | 0% | 3 |
Monitoring and Reporting
Administrative requirements. No direct health risk from the violation itself.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Public Notification Rule | 7500 | 207 | 7% | 207 |
| Consumer Confidence Rule (CCR) | 7000 | 78 | 3% | 78 |
Volatile Organic Compound
Solvents and fuel components, usually monitored as a group, which is why the counts are similar.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| 1,2,4-Trichlorobenzene | 2378 | 34 | 1% | 2 |
| cis-1,2-Dichloroethylene | 2380 | 34 | 1% | 2 |
| Xylenes, Total | 2955 | 34 | 1% | 2 |
| Dichloromethane (Methylene Chloride) | 2964 | 34 | 1% | 2 |
| o-Dichlorobenzene | 2968 | 34 | 1% | 2 |
| p-Dichlorobenzene | 2969 | 34 | 1% | 2 |
| Vinyl Chloride | 2976 | 34 | 1% | 2 |
| 1,1-Dichloroethylene | 2977 | 34 | 1% | 2 |
| trans-1,2-Dichloroethylene | 2979 | 34 | 1% | 2 |
| 1,2-Dichloroethane | 2980 | 34 | 1% | 2 |
| 1,1,1-Trichloroethane | 2981 | 34 | 1% | 2 |
| Carbon Tetrachloride | 2982 | 34 | 1% | 2 |
| 1,2-Dichloropropane | 2983 | 34 | 1% | 2 |
| Trichloroethylene (TCE) | 2984 | 34 | 1% | 2 |
| 1,1,2-Trichloroethane | 2985 | 34 | 1% | 2 |
| Tetrachloroethylene (PCE) | 2987 | 34 | 1% | 2 |
| Chlorobenzene | 2989 | 34 | 1% | 2 |
| Benzene | 2990 | 34 | 1% | 2 |
| Toluene | 2991 | 34 | 1% | 2 |
| Ethylbenzene | 2992 | 34 | 1% | 2 |
| Styrene | 2996 | 34 | 1% | 2 |
Organic Chemical
Industrial and synthetic organic chemicals with a maximum contaminant level.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Pentachlorophenol | 2326 | 19 | 1% | 1 |
| Hexachlorocyclopentadiene | 2042 | 16 | 1% | 1 |
| Hexachlorobenzene | 2274 | 16 | 1% | 1 |
| 2,3,7,8-TCDD (Dioxin) | 2063 | 1 | 0% | 0 |
Pesticide
Pesticides and herbicides, monitored as a group.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Atrazine | 2050 | 21 | 1% | 2 |
| Simazine | 2037 | 20 | 1% | 1 |
| Alachlor (Lasso) | 2051 | 20 | 1% | 1 |
| Dalapon | 2031 | 19 | 1% | 1 |
| Picloram | 2040 | 19 | 1% | 1 |
| Dinoseb | 2041 | 19 | 1% | 1 |
| 2,4-D | 2105 | 19 | 1% | 1 |
| 2,4,5-TP (Silvex) | 2110 | 19 | 1% | 1 |
| Endrin | 2005 | 16 | 1% | 1 |
| BHC-Gamma (Lindane) | 2010 | 16 | 1% | 1 |
| Methoxychlor | 2015 | 16 | 1% | 1 |
| Toxaphene | 2020 | 16 | 1% | 1 |
| Oxamyl (Vydate) | 2036 | 16 | 1% | 1 |
| Aldicarb Sulfoxide | 2043 | 16 | 1% | 1 |
| Aldicarb Sulfone | 2044 | 16 | 1% | 1 |
| Carbofuran | 2046 | 16 | 1% | 1 |
| Aldicarb | 2047 | 16 | 1% | 1 |
| Heptachlor | 2065 | 16 | 1% | 1 |
| Heptachlor Epoxide | 2067 | 16 | 1% | 1 |
| Chlordane | 2959 | 16 | 1% | 1 |
Radionuclide
Naturally occurring radioactive elements in groundwater.
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Radium-228 | 4030 | 8 | 0% | 0 |
| Radium-226 | 4020 | 7 | 0% | 0 |
| Combined Radium (-226 and -228) | 4010 | 7 | 0% | 1 |
| Combined Uranium | 4006 | 1 | 0% | 0 |
Other rules
| Rule or contaminant | Code | Missouri systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Carbon, Total | 2920 | 6 | 0% | 2 |
| Chlorine dioxide | 1008 | 3 | 0% | 0 |
About this data
A system is counted once per rule if any of its violations in the past three years involved that rule, including monitoring and reporting lapses. Unresolved means still in violation at EPA's latest data refresh. Share is of the 2,835 active Missouri systems.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The Missouri records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet. Retrieved from ECHO on Oct 11, 2026.