What is Propene* and Why Does It Matter?

Propene (also called propylene) is a colorless gas that can dissolve into water supplies near industrial areas. It belongs to a family of chemicals called alkenes — simple hydrocarbons used heavily in manufacturing. Refineries, petrochemical plants, and plastics production facilities all release propene as a byproduct. It can enter drinking water through industrial discharge, stormwater runoff, or leaks near processing facilities. The asterisk often attached to its name in water testing data signals that detection methods may have some uncertainty, so reported levels should be interpreted carefully.

At 0.7 parts per billion (ppb), the concentration detected in affected water systems sits at a low level. Current research on propene's health effects in drinking water is limited compared to more extensively studied contaminants. At high concentrations — primarily through air exposure in industrial settings — propene can cause dizziness, headaches, and respiratory irritation. Long-term, high-dose animal studies have raised some questions about potential effects on the liver and nervous system, but the evidence at drinking water concentrations is not well established. The World Health Organization (WHO) has not set a specific drinking water guideline for propene, which reflects both its limited occurrence and the gaps in available health data.

The EPA has not established a Maximum Contaminant Level (MCL) for propene in drinking water. That means there is no federal legal limit that water utilities must meet. The Environmental Working Group (EWG) also does not currently publish a specific health guideline for propene, which makes it harder for consumers to benchmark detected levels against a safety threshold. The 0 systems reported above any guideline in this dataset reflects that absence of a standard — not necessarily a confirmation that detected levels are safe. When regulators haven't set limits, it doesn't mean there's no reason to pay attention. It means the science is still catching up.

Geographically, all 23 water systems where propene has been detected are located in Texas. That pattern makes sense. Texas is home to one of the largest concentrations of oil refineries, petrochemical plants, and plastics manufacturers in the United States. The Gulf Coast corridor — running from Houston through Beaumont and Port Arthur — processes enormous volumes of petroleum products daily. Propene is a direct byproduct of oil refining and natural gas processing. Communities near these industrial corridors face a higher likelihood of trace industrial chemicals appearing in their water supply. Rural water systems with less treatment infrastructure may be especially vulnerable to these kinds of industrial trace compounds.

If you're in Texas — particularly near industrial areas — it's worth taking a closer look at your water quality report. A reverse osmosis (RO) filtration system is generally the most effective option for removing dissolved hydrocarbons like propene from tap water. RO systems force water through a semi-permeable membrane that blocks contaminants at the molecular level, removing up to 99% of many chemical compounds. Activated carbon filters also help reduce hydrocarbon-based contaminants and can serve as a strong first line of defense. Echo Water's systems combine both technologies, which gives you layered protection even against contaminants that lack official regulatory limits. Knowing a contaminant exists in your water — even at low levels — is exactly the kind of information that helps you make a smarter decision about filtration. You don't need to panic. You just need a plan.

Regulatory Standards for Propene*

Cities With the Highest Propene* Levels

States Most Affected by Propene*

Frequently Asked Questions

Related Contaminant Guides