Naphthalene: The Contaminant in Tap Water You Didn't Know Was Harming Your Health

Written by Craig "The Water Guy" Phillips

Naphthalene, the chemical best known from mothballs, is not a common tap water contaminant, but it can show up in groundwater and wells near petroleum spills, leaking fuel tanks, coal tar and former gas plant sites. The EPA does not have an enforceable limit for it in drinking water; instead it has a non-enforceable lifetime health advisory of 100 micrograms per liter (0.1 mg/L), and the standard home treatment is activated carbon filtration.

If your water has a mothball or fuel-like odor, or your well is near a known petroleum or industrial site, a lab test for volatile organic compounds (VOCs) is the way to find out. Below we cover where naphthalene comes from, what it does to health, how it's tested and how to reduce it.

Understanding Naphthalene and Its Presence in Water Systems

Naphthalene is a white, crystalline compound with a strong mothball odor. It is the simplest polycyclic aromatic hydrocarbon (PAH), made of two fused benzene rings, and it occurs naturally in crude oil and coal tar. It is also produced for industrial uses such as making dyes, resins and other chemicals.

It dissolves in water only slightly, but enough to matter where there is a source nearby. It is also volatile, which means it evaporates from water fairly easily. That has two consequences at home: some naphthalene escapes from open water, and some can be inhaled when contaminated water is heated or sprayed, such as in a shower. In soil and groundwater it tends to break down over time, but it can persist where a large source like a fuel spill keeps feeding it in.

Primary Sources of Naphthalene Contamination in Drinking Water

Most naphthalene that reaches drinking water comes from petroleum and coal-based sources:

• Leaking underground storage tanks and fuel spills. Gasoline, diesel and heating oil contain naphthalene, so leaking tanks and spills are among the most common sources for private wells.
• Coal tar and former manufactured gas plants. Older sites that made gas from coal, along with coking operations, can leave coal tar in the ground that leaches into groundwater for decades.
• Petroleum refining and chemical manufacturing. Industrial discharges and spills can reach rivers and aquifers.
• Combustion. Vehicle exhaust, wood smoke and other burning release naphthalene to air, though the amounts that reach water this way are usually small.
• Household products. Mothballs, some coal-tar based sealants and wood preservatives can add naphthalene locally, typically at low levels.

Public water systems that draw from surface water are less likely to see it than shallow private wells near a fuel or industrial source. If you want a full picture of what's in your water, our guide to well water filtration and softening explains how to match treatment to your test results.

Health Effects and Risks Associated with Naphthalene Exposure

The best-documented health effect of high naphthalene exposure is hemolytic anemia, where red blood cells break down faster than the body can replace them. Most reported cases involve swallowing mothballs or heavy exposure to vapors, not drinking water. People with glucose-6-phosphate dehydrogenase (G6PD) deficiency and newborns are especially sensitive.

Symptoms of high short-term exposure can include nausea, vomiting, diarrhea, headache and fatigue. Animal studies have linked long-term exposure to effects on the eyes (cataracts) and other organs. The International Agency for Research on Cancer (IARC) classifies naphthalene as possibly carcinogenic to humans (Group 2B), based mainly on animal inhalation studies.

For drinking water, the practical takeaway is this: low-level detections are a reason to find the source and treat, not to panic. If you're concerned about a specific exposure, especially for an infant or someone with G6PD deficiency, talk with your doctor.

Detection Methods and Regulatory Standards for Naphthalene

Naphthalene is measured by certified labs using gas chromatography-mass spectrometry (GC-MS), usually as part of a volatile organic compound (VOC) panel. These methods detect it at parts-per-billion levels. A standard home test kit or a basic "minerals and bacteria" panel will not include it, so you need to ask for a VOC test specifically.

Because there is no federal limit, public water systems are not routinely required to test for naphthalene, and private wells are never tested unless the owner orders it. Consider a VOC test if your well is near a gas station, fuel storage, a former gas plant or an industrial site, if you've had a fuel oil or gasoline spill, or if you notice a mothball or fuel odor in your water.

Treatment and Prevention Strategies for Naphthalene Contamination

Activated carbon is the standard treatment for naphthalene. Naphthalene adsorbs readily onto granular activated carbon (GAC) and carbon block, which is why carbon is used both by utilities and in home systems for this group of chemicals.

• Whole-house carbon filtration treats every tap, which matters for a volatile chemical you can also inhale in the shower. Options include the SoftPro Chlorine+ catalytic carbon filter for city water and the SoftPro catalytic carbon filter for well water . Ask us to size the system to your test results and flow rate.
• Point-of-use filtration such as an under-sink reverse osmosis system with carbon stages adds protection for drinking and cooking water. See combining a softener with RO or UV for how these fit together.
• Aeration (air stripping) removes volatile chemicals and is used where contamination is high, often alongside carbon.

Whatever you choose, look for performance data or certification that covers VOC reduction, replace carbon on schedule (spent carbon stops adsorbing), and retest after installation to confirm results. A water softener does not remove naphthalene; if you're adding carbon to an existing softener, see pairing a water softener with a carbon filter .

Prevention comes down to keeping sources out of the ground: dispose of fuel, solvents and mothballs properly, maintain fuel oil tanks, and report spills near wells. If the contamination comes from a nearby site, your state environmental agency can tell you whether it is being investigated. For other metals and chemicals in tap water, see our guide to nickel in tap water .

Frequently Asked Questions About Naphthalene in Drinking Water