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Data sourced from EPA SDWIS & USGS.

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Coliform Bacteria in Well Water by State

Indicates possible contamination from surface water or sewage.

Category

biological

EPA Limit (MCL)

0 present/absent

States Tracked

51

Live DataLast updated: April 4, 2026·Source: EPA SDWIS & USGS

Top 10 Highest Risk States

Highest % of wells exceeding EPA limits for Coliform Bacteria

#1 Iowa9.9%#2 Texas9.7%#3 New Mexico9.4%#4 North Dakota9.1%#5 Alabama8.6%#6 Minnesota7.9%#7 South Carolina7.5%#8 South Dakota7.2%#9 Michigan7.0%#10 Maryland6.9%

Top 10 Cleanest States

Lowest % of wells exceeding EPA limits for Coliform Bacteria

#1 Massachusetts0.4%#2 Utah0.5%#3 Arizona0.7%#4 Illinois0.8%#5 Oregon1.0%#6 Pennsylvania1.3%#7 Rhode Island1.5%#8 Maine1.6%#9 Nebraska1.8%#10 Vermont1.8%

Coliform Bacteria in Every State

AlabamaAL · Score: 68/100 AlaskaAK · Score: 55/100 ArizonaAZ · Score: 72/100 ArkansasAR · Score: 62/100 CaliforniaCA · Score: 75/100 ColoradoCO · Score: 70/100 ConnecticutCT · Score: 78/100 DelawareDE · Score: 72/100 District of ColumbiaDC · Score: 85/100 FloridaFL · Score: 65/100 GeorgiaGA · Score: 67/100 HawaiiHI · Score: 80/100 IdahoID · Score: 73/100 IllinoisIL · Score: 71/100 IndianaIN · Score: 66/100 IowaIA · Score: 64/100 KansasKS · Score: 68/100 KentuckyKY · Score: 63/100 LouisianaLA · Score: 61/100 MaineME · Score: 72/100 MarylandMD · Score: 74/100 MassachusettsMA · Score: 79/100 MichiganMI · Score: 68/100 MinnesotaMN · Score: 71/100 MississippiMS · Score: 59/100 MissouriMO · Score: 65/100 MontanaMT · Score: 76/100 NebraskaNE · Score: 69/100 NevadaNV · Score: 70/100 New HampshireNH · Score: 75/100 New JerseyNJ · Score: 73/100 New MexicoNM · Score: 64/100 New YorkNY · Score: 76/100 North CarolinaNC · Score: 69/100 North DakotaND · Score: 67/100 OhioOH · Score: 70/100 OklahomaOK · Score: 63/100 OregonOR · Score: 77/100 PennsylvaniaPA · Score: 72/100 Rhode IslandRI · Score: 76/100 South CarolinaSC · Score: 66/100 South DakotaSD · Score: 68/100 TennesseeTN · Score: 64/100 TexasTX · Score: 66/100 UtahUT · Score: 74/100 VermontVT · Score: 78/100 VirginiaVA · Score: 71/100 WashingtonWA · Score: 76/100 West VirginiaWV · Score: 58/100 WisconsinWI · Score: 72/100 WyomingWY · Score: 71/100

EPA SDWIS & USGS

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