What is Naphthalene* and Why Does It Matter?

Naphthalene is a chemical compound most people recognize from mothballs — that sharp, distinctive smell in old closets. It also forms naturally when coal, oil, and wood burn incompletely. Industrial facilities, gas stations, and coal tar processing plants release naphthalene into the environment, where it can seep into groundwater and eventually reach drinking water systems. Runoff from contaminated soil near industrial sites is one of the most common pathways into public water supplies.

Across the United States, 23 water systems have detected naphthalene in their tap water. The average level found is 0.251 parts per billion (ppb), with the highest recorded level reaching 2.3 ppb. While those numbers may sound small, the concern isn't necessarily a single glass of water — it's long-term, repeated exposure over months and years.

Health researchers have linked naphthalene exposure to several serious conditions. The International Agency for Research on Cancer (IARC) classifies naphthalene as a possible human carcinogen, meaning there's credible evidence it may cause cancer with sustained exposure. Animal studies show it can damage red blood cells, leading to a condition called hemolytic anemia. The liver and eyes are also vulnerable organs. Children and people with a genetic enzyme deficiency called G6PD are especially sensitive to naphthalene's effects, according to the Agency for Toxic Substances and Disease Registry (ATSDR). Short-term high-dose exposure can cause nausea, fatigue, and confusion.

The EPA has set a maximum contaminant level (MCL) for naphthalene at 100 ppb — a legal limit that water utilities must stay below. Importantly, none of the 23 systems detected above that legal threshold. However, the EPA's MCL was established primarily around acute toxicity, not long-term cancer risk. The Environmental Working Group (EWG) applies a stricter standard based on cancer risk assessments, and at 2.3 ppb — the highest level found in this dataset — some health advocates argue that meaningful risk accumulates over a lifetime of drinking water consumption. The gap between the legal limit and what health researchers consider truly safe is worth understanding.

Geographically, Arkansas accounts for the vast majority of detections, with 20 of the 23 affected systems located there. Virginia shows 2 detections, and Oklahoma accounts for 1. Arkansas's pattern likely reflects the state's industrial history and the presence of oil and gas infrastructure, which are known sources of naphthalene contamination. Coal tar deposits and petroleum processing facilities leave long-lasting chemical footprints in the surrounding soil and groundwater. Rural water systems in these regions often draw from groundwater sources that sit closer to legacy contamination sites, giving them less natural dilution than large surface water systems.

The good news is that naphthalene is removable. Activated carbon filtration — the kind found in many under-sink and whole-house filters — is effective at reducing naphthalene levels in drinking water. Granular activated carbon (GAC) works by attracting and trapping organic compounds like naphthalene as water passes through. For the most thorough protection, a reverse osmosis (RO) system combined with activated carbon removes a broad range of organic contaminants, including naphthalene, down to very low levels. Echo Water's systems use multi-stage filtration that includes activated carbon specifically designed to target volatile organic compounds (VOCs) like naphthalene. If you live in Arkansas, Virginia, or Oklahoma — or near any industrial or petroleum facility — it's worth testing your water first to understand your actual exposure level before choosing a filter. Knowing your numbers makes the solution much clearer.

Regulatory Standards for Naphthalene*

Cities With the Highest Naphthalene* Levels

States Most Affected by Naphthalene*

Frequently Asked Questions

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