What is MTBE* and Why Does It Matter?

MTBE (methyl tertiary-butyl ether) is a fuel additive that was widely used in gasoline throughout the 1990s and early 2000s. The EPA required it to reduce air pollution from car exhaust. The problem? MTBE dissolves easily in water and doesn't break down quickly in the environment. When gasoline leaks from underground storage tanks, pipelines, or spills at gas stations, MTBE travels straight into groundwater — and eventually into drinking water supplies. Even small amounts can make water smell and taste like turpentine or gasoline.

The health picture with MTBE is still developing, but the early evidence is concerning. Animal studies show that high doses cause kidney, liver, and nervous system damage (National Toxicology Program). The EPA classifies MTBE as a possible human carcinogen, meaning it may cause cancer with long-term exposure. At lower levels — like the 0.672 ppb average detected across 23 water systems in this dataset — most people won't notice any immediate effects. But long-term, low-level exposure is exactly the kind of risk that's hard to see coming. Children and pregnant women are generally considered more vulnerable to chemical contaminants in drinking water.

The regulatory situation around MTBE is frustratingly incomplete. The EPA has not set a legally enforceable maximum contaminant level (MCL) for MTBE in drinking water. Instead, the agency offers an informal guidance range of 20 to 40 ppb based on taste and odor — not health protection. The good news in this dataset is that none of the 23 systems detected MTBE above even that loose guideline. The highest reading was 2.46 ppb, well below the EPA's advisory range. That said, "below the guideline" doesn't automatically mean "safe." Many scientists argue the current guidance is outdated and doesn't reflect what we now know about long-term chemical exposure.

Geographically, MTBE contamination follows a clear pattern tied to industrial history and underground fuel storage. Delaware and Arkansas each show 4 affected systems, leading the dataset. Rhode Island has 3, while Indiana and New Jersey each report 2. These states share something in common: aging underground storage tank infrastructure and, in some cases, dense concentrations of gas stations and industrial facilities near water sources. The Northeast, in particular, dealt with widespread MTBE use during the reformulated gasoline program of the 1990s. Many states have since banned MTBE in gasoline — California did so in 2004, and federal use dropped sharply after that — but contamination can linger in groundwater for years, even decades, after the source is gone.

The most effective way to remove MTBE from drinking water is activated carbon filtration, specifically granular activated carbon (GAC) or solid block carbon filters. These work by attracting and trapping MTBE molecules as water passes through. Reverse osmosis (RO) systems also reduce MTBE, though activated carbon tends to be the stronger performer for this particular contaminant. If you're in Delaware, Arkansas, Rhode Island, Indiana, or New Jersey — or anywhere with older gas station infrastructure nearby — it's worth knowing what's in your water before assuming it's clean. A certified home water test can tell you exactly what you're dealing with. From there, a quality under-sink carbon filter or a whole-home filtration system from Echo Water can give you reliable, ongoing protection. The goal isn't to scare you — it's to make sure you're not drinking something you didn't sign up for.

Regulatory Standards for MTBE*

Cities With the Highest MTBE* Levels

States Most Affected by MTBE*

Frequently Asked Questions

Related Contaminant Guides