Contaminants and rules in Connecticut water systems
83 different rules and contaminants appear in the past three years of violation records for Connecticut's 2,334 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 | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Revised Total Coliform Rule (RTCR) | 8000 | 466 | 20% | 161 |
| E. coli (Escherichia coli) | 3014 | 119 | 5% | 64 |
Inorganic Chemical
Naturally occurring or from fertilizer and industry. Each has a maximum contaminant level.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Nitrate | 1040 | 130 | 6% | 8 |
| Nitrite | 1041 | 90 | 4% | 2 |
| Arsenic | 1005 | 25 | 1% | 2 |
| Cyanide | 1024 | 21 | 1% | 0 |
| Mercury | 1035 | 18 | 1% | 0 |
| Barium | 1010 | 17 | 1% | 0 |
| Cadmium | 1015 | 17 | 1% | 0 |
| Chromium | 1020 | 17 | 1% | 0 |
| Fluoride | 1025 | 17 | 1% | 0 |
| Nickel | 1036 | 17 | 1% | 0 |
| Selenium | 1045 | 17 | 1% | 0 |
| Antimony | 1074 | 17 | 1% | 0 |
| Beryllium | 1075 | 17 | 1% | 0 |
| Thallium | 1085 | 17 | 1% | 0 |
| Asbestos | 1094 | 4 | 0% | 0 |
Disinfection Byproduct
Formed when chlorine reacts with organic matter in the water.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| TTHM (Total Trihalomethanes) | 2950 | 23 | 1% | 3 |
| Total Haloacetic Acids (HAA5) | 2456 | 19 | 1% | 2 |
| Chlorite | 1009 | 1 | 0% | 0 |
Treatment Technique
Rules that require a process, such as corrosion control or disinfection, rather than a measured limit.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Lead and Copper Rule Revisions (LCRR) | 5200 | 319 | 14% | 319 |
| Lead and Copper Rule (LCR) | 5000 | 123 | 5% | 122 |
| Groundwater Rule (GWR) | 0700 | 32 | 1% | 28 |
| Chlorine (MRDL) | 0999 | 22 | 1% | 6 |
| Surface Water Treatment Rule (SWTR) | 0200 | 3 | 0% | 1 |
| Interim Enhanced Surface Water Treatment Rule | 0300 | 1 | 0% | 0 |
Monitoring and Reporting
Administrative requirements. No direct health risk from the violation itself.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Public Notification Rule | 7500 | 272 | 12% | 272 |
| Consumer Confidence Rule (CCR) | 7000 | 30 | 1% | 30 |
Volatile Organic Compound
Solvents and fuel components, usually monitored as a group, which is why the counts are similar.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Tetrachloroethylene (PCE) | 2987 | 43 | 2% | 4 |
| Dichloromethane (Methylene Chloride) | 2964 | 42 | 2% | 4 |
| trans-1,2-Dichloroethylene | 2979 | 42 | 2% | 4 |
| Trichloroethylene (TCE) | 2984 | 42 | 2% | 4 |
| Ethylbenzene | 2992 | 42 | 2% | 4 |
| 1,1-Dichloroethylene | 2977 | 40 | 2% | 4 |
| 1,2,4-Trichlorobenzene | 2378 | 39 | 2% | 4 |
| cis-1,2-Dichloroethylene | 2380 | 39 | 2% | 4 |
| o-Dichlorobenzene | 2968 | 39 | 2% | 4 |
| p-Dichlorobenzene | 2969 | 39 | 2% | 4 |
| Vinyl Chloride | 2976 | 39 | 2% | 4 |
| 1,2-Dichloroethane | 2980 | 39 | 2% | 4 |
| 1,1,1-Trichloroethane | 2981 | 39 | 2% | 4 |
| Carbon Tetrachloride | 2982 | 39 | 2% | 4 |
| 1,2-Dichloropropane | 2983 | 39 | 2% | 4 |
| 1,1,2-Trichloroethane | 2985 | 39 | 2% | 4 |
| Chlorobenzene | 2989 | 39 | 2% | 4 |
| Benzene | 2990 | 39 | 2% | 4 |
| Toluene | 2991 | 39 | 2% | 4 |
| Styrene | 2996 | 39 | 2% | 4 |
| Ethylene Dibromide (EDB) | 2946 | 34 | 1% | 1 |
Organic Chemical
Industrial and synthetic organic chemicals with a maximum contaminant level.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Di(2-ethylhexyl) Phthalate | 2039 | 41 | 2% | 2 |
| Di(2-ethylhexyl) Adipate | 2035 | 34 | 1% | 1 |
| Benzo(a)pyrene | 2306 | 34 | 1% | 1 |
| 1,2-Dibromo-3-Chloropropane (DBCP) | 2931 | 33 | 1% | 1 |
| Hexachlorocyclopentadiene | 2042 | 31 | 1% | 1 |
| Hexachlorobenzene | 2274 | 31 | 1% | 1 |
| Polychlorinated Biphenyls (PCBs) | 2383 | 31 | 1% | 2 |
| Pentachlorophenol | 2326 | 30 | 1% | 1 |
Pesticide
Pesticides and herbicides, monitored as a group.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Oxamyl (Vydate) | 2036 | 35 | 1% | 1 |
| Aldicarb Sulfoxide | 2043 | 35 | 1% | 1 |
| Aldicarb Sulfone | 2044 | 35 | 1% | 1 |
| Carbofuran | 2046 | 35 | 1% | 1 |
| Aldicarb | 2047 | 35 | 1% | 1 |
| Diquat | 2032 | 34 | 1% | 1 |
| Glyphosate | 2034 | 34 | 1% | 1 |
| Simazine | 2037 | 33 | 1% | 1 |
| Atrazine | 2050 | 33 | 1% | 1 |
| Toxaphene | 2020 | 32 | 1% | 1 |
| Endrin | 2005 | 31 | 1% | 1 |
| BHC-Gamma (Lindane) | 2010 | 31 | 1% | 1 |
| Methoxychlor | 2015 | 31 | 1% | 1 |
| Alachlor (Lasso) | 2051 | 31 | 1% | 1 |
| Heptachlor | 2065 | 31 | 1% | 1 |
| Heptachlor Epoxide | 2067 | 31 | 1% | 1 |
| Dalapon | 2031 | 30 | 1% | 1 |
| Picloram | 2040 | 30 | 1% | 1 |
| Dinoseb | 2041 | 30 | 1% | 1 |
| 2,4-D | 2105 | 30 | 1% | 1 |
| 2,4,5-TP (Silvex) | 2110 | 30 | 1% | 1 |
| Chlordane | 2959 | 30 | 1% | 1 |
Radionuclide
Naturally occurring radioactive elements in groundwater.
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Gross Alpha, Excl. Radon and U | 4000 | 10 | 0% | 1 |
| Combined Uranium | 4006 | 10 | 0% | 1 |
| Combined Radium (-226 and -228) | 4010 | 10 | 0% | 1 |
Other rules
| Rule or contaminant | Code | Connecticut systems with violations, 3 yr | Share | Unresolved |
|---|---|---|---|---|
| Carbon, Total | 2920 | 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 2,334 active Connecticut 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 Connecticut 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.