The EPA allows up to 4mg/L of chlorine in municipal water supplies. That's the same concentration used in public swimming pools. Every shower you take exposes your skin and lungs to that chlorine, along with dozens of other chemicals most people never think about.
Your tap water travels through miles of aging infrastructure before reaching your home. Along the way, it collects treatment chemicals, mineral deposits, and trace contaminants that affect everything from your skin health to how your soap performs.
Municipal tap water in the United States contains regulated levels of chlorine, fluoride, disinfection byproducts, and trace heavy metals. While legally safe to drink, these substances affect skin and hair through dermal absorption and inhalation during hot showers, where chlorine vaporizes in enclosed spaces.
The EPA's Water Quality Standards
The Safe Drinking Water Act regulates 90 contaminants in U.S. tap water. But "regulated" doesn't mean "absent." It means levels are monitored and kept below maximum contaminant levels (MCLs).
Those MCLs are set based on what's technically feasible for water treatment facilities to achieve, not necessarily what's optimal for your health. A 2019 USGS study found that 45% of tap water samples contained at least one contaminant above the health guideline threshold, even when below the legal limit.
The difference matters. Legal limits allow for trace amounts of substances you'd probably prefer to avoid entirely.
Common Contaminants in Municipal Water
Municipal water treatment removes most dangerous bacteria and viruses. But the treatment process itself introduces new substances, and distribution systems add others.
Chlorine and chloramine are added intentionally to kill bacteria. Chlorine concentrations range from 0.5 to 2.0 mg/L in most systems, with the EPA maximum set at 4 mg/L. When chlorine hits hot water in your shower, it vaporizes. You breathe it in. You absorb it through your skin, which is especially permeable when warm and wet.
Fluoride is added in most municipal systems at 0.7 mg/L to support dental health. Some people seek it out. Others prefer to filter it.
Disinfection byproducts form when chlorine reacts with organic matter in source water. Trihalomethanes (THMs) and haloacetic acids (HAAs) are the most common. EPA allows up to 80 parts per billion (ppb) for total THMs and 60 ppb for HAAs. Research published in Environmental Health Perspectives linked long-term exposure to increased bladder cancer risk.
Heavy metals leach from pipes and plumbing fixtures. Lead is the most notorious. The EPA's action level is 15 ppb, but the American Academy of Pediatrics states no level of lead exposure is safe for children. Copper can leach from pipes at levels up to 1.3 mg/L.
Hard water minerals (calcium and magnesium) aren't health hazards. But they're cosmetic nuisances that affect 85% of American homes, according to the Water Quality Association. These minerals form scale, reduce soap effectiveness, and leave residue on skin and hair. If you've noticed buildup on your fixtures, our guide on how to identify hard water in your shower covers the common signs.
Chlorine: The Most Overlooked Threat in Showers
Drinking chlorinated water exposes you to roughly 8 ounces of liquid daily. Showering in chlorinated water exposes you to vaporized chlorine through inhalation and dermal absorption for 8-10 minutes.
A 1986 study in the American Journal of Public Health found that people absorb more chlorine from a 10-minute shower than from drinking 8 glasses of the same water. Hot water opens pores. Chlorine vapor concentrates in enclosed shower spaces. You're breathing it directly into your lungs.
Chlorine strips the natural oils (lipids) that protect your skin barrier. That's why your skin feels tight or dry after chlorinated showers. It oxidizes proteins in your hair, making it brittle and discolored over time. Blonde hair can even take on a greenish tint from copper-chlorine reactions. We cover the full science behind this in our piece on why chlorine in shower water matters.
For people with eczema, psoriasis, or sensitive skin, chlorine exposure can trigger flare-ups. Asthma patients often report that chlorine vapor irritates their airways.
The science backs up what your skin already knows.
Heavy Metals and Mineral Deposits
Lead doesn't come from the treatment plant. It comes from your home's plumbing. Homes built before 1986 often have lead solder in pipe joints. Even "lead-free" brass fixtures can leach small amounts of lead, especially in corrosive water.
The Flint, Michigan crisis brought lead contamination into national awareness in 2014. But low-level lead exposure happens in thousands of homes where residents never suspect it. EPA data shows that 10-20% of total lead exposure comes from drinking water alone.
Copper pipes are common in modern plumbing. When water sits in pipes overnight, copper can leach into the first draw. Levels spike in new construction during the first year as pipes "season." Blue-green stains on fixtures are a visual indicator of copper leaching.
Hard water minerals create a different problem. Calcium and magnesium don't pose health risks, but they react with soap to form an insoluble film. This film clings to skin and hair, leaving residue that soap and shampoo can't fully rinse away. Over time, mineral buildup clogs shower heads, reduces water pressure, and shortens the lifespan of appliances. If you're dealing with hard water damage to your hair, the mineral film is usually the root cause.
Water hardness above 120 mg/L is considered "hard" by USGS standards. Many regions in the Southwest, Midwest, and Great Plains exceed 180 mg/L, classified as "very hard."
What This Means for Your Shower
Your shower water is treated drinking water. It meets federal safety standards for ingestion. But showering involves different exposure pathways: heat, vapor, extended skin contact. Drinking doesn't expose you the same way.
Hot water amplifies everything. It opens pores, increases absorption, and turns volatile chemicals like chlorine into breathable vapor. An enclosed shower stall concentrates that vapor.
That's why shower filtration exists as a separate category from drinking water filters. Multi-stage filtered shower heads like the StoneStream EcoPower use media like KDF (Kinetic Degradation Fluxion) and activated carbon to reduce chlorine, heavy metals, and some dissolved solids before water reaches your body. They address the dermal and inhalation exposure that drinking water filters don't.
Whether you need one depends on your water quality and your sensitivity. If your skin feels dry, your hair looks dull, or you smell chlorine when you shower, filtration changes the experience noticeably.
Frequently Asked Questions
Is tap water safe to shower in?
Tap water meets EPA safety standards for pathogens and toxins. But "safe" and "optimal" aren't the same thing. Chlorine, hard water minerals, and trace heavy metals won't make you sick in the short term, but they affect skin health, hair condition, and comfort over time.
How do I know what's in my tap water?
Every municipal water system publishes an annual Consumer Confidence Report (CCR) listing detected contaminants and their levels. You can find yours by searching "[your city name] water quality report" or visiting the EPA's CCR database. For well water or more detailed testing, independent labs analyze samples for $100-300.
Does boiling water remove chlorine and contaminants?
Boiling removes chlorine through evaporation and kills bacteria, but it concentrates heavy metals and minerals. Calcium and lead don't evaporate. They stay in the water as volume reduces. For drinking, boiling works for disinfection. For showers, it's impractical.
Are chlorine levels in tap water dangerous?
At EPA-regulated levels (under 4 mg/L), chlorine in tap water isn't acutely toxic. Long-term exposure to disinfection byproducts carries some risk (see EPA and research data above). The bigger issue for most people is skin irritation, dryness, and respiratory irritation from chlorine vapor during showers.
