Chlorine and disinfection byproducts: why your shower matters most

Chlorine keeps public water safe, and that is genuinely a good thing. But the chlorine used to disinfect your water also creates a family of byproducts called trihalomethanes, or TTHMs, and here is the part almost no one is told: for these particular contaminants, the water you drink may not be your biggest exposure at all. Your shower is.

What disinfection byproducts are

To keep water safe on its journey from the treatment plant to your home, utilities add a disinfectant, usually chlorine or chloramine. When that chlorine meets the natural organic matter present in surface water, like the water Phoenix draws from the Salt, Verde and Colorado Rivers, it reacts and forms disinfection byproducts (DBPs). The two groups the EPA regulates are:

• Trihalomethanes (TTHMs), reported together as Total Trihalomethanes, a group that includes chloroform.
• Haloacetic acids (HAA5), a second group of five regulated acids.

They are, in a sense, the price of safe water: the same disinfection that protects you from bacteria produces a byproduct with its own long-term concerns. The goal is not to remove the chlorine at the plant, it is to remove these byproducts and the leftover chlorine before they reach the inside of your home.

The exposure almost everyone misses: your shower

This is the heart of it. TTHMs are volatile, meaning they evaporate easily, and they move into your body through more than your mouth. In a hot shower, two routes open at once:

• Inhalation. Hot water and steam drive the TTHMs out of the water and into the air of an enclosed bathroom, where you breathe them straight in. That "pool smell" in a hot shower is you inhaling volatilized chlorine and its byproducts.
• Skin absorption. Warm water opens your pores and your skin absorbs these compounds directly over the several minutes you stand under it.

The research here is striking. Studies measuring chloroform (a TTHM) in people's breath and blood have found that levels rise sharply after a shower, and that inhalation and skin absorption during showering and bathing can contribute as much exposure as drinking the water, or more. A hot ten-minute shower in a closed bathroom is, for volatile DBPs, close to a worst-case scenario. It is why treating only the kitchen drinking tap leaves the single largest exposure route completely untouched.

The health concerns

Because DBPs are consumed and absorbed daily over years, the concern is long-term exposure. Drawing on the EPA and published research:

• Bladder cancer has the most consistent association in the epidemiology, long-term exposure to disinfection byproducts has been repeatedly linked to increased bladder cancer risk. Some studies also examine possible links to colorectal cancer.
• Several individual trihalomethanes are classified by the WHO's cancer agency (IARC) as possibly carcinogenic to humans, and the EPA's health goal (MCLG) for some of them, such as bromodichloromethane and bromoform, is set at zero.
• Reproductive and developmental effects. A body of research has investigated associations between high DBP exposure during pregnancy and outcomes such as low birth weight; findings are mixed but the concern is taken seriously enough to keep the limits strict.

As with every contaminant, the enforceable legal limit and the health goal are two different numbers, a distinction we cover in legal versus ideal. The EPA's enforceable limit for TTHMs is 80 parts per billion. Phoenix-area water has been reported at roughly 38 parts per billion in the EWG Tap Water Database, comfortably legal, and still many times above the zero health goal set for the most concerning byproducts.

The cosmetic toll: skin, hair and eyes

Long before any of that, chlorinated water and its byproducts do something you can see and feel every day. Chlorine is designed to break things down, and it does not stop at bacteria:

• Dry, tight, itchy skin. Chlorine strips the natural oils that keep your skin's barrier intact, leaving it dry and irritated, and it can aggravate eczema, psoriasis and sensitive skin.
• Dull, brittle hair. The same oil-stripping effect leaves hair dry and straw-like, roughens the cuticle, and can fade and brassily shift color-treated hair, the reason it is often compared to swimming-pool hair.
• Irritated eyes and scalp. That faint sting and the tight, flaky scalp after a shower are familiar signs of chlorinated water.
• The smell and taste. The chemical "pool" note in the water and in the air of the shower is chlorine and its byproducts, plain and simple.

People who switch to dechlorinated, filtered water throughout the home very often describe softer skin, more manageable hair and calmer, less itchy showers within days. It is the most immediately noticeable benefit of treating this at every tap.

How to remove them: carbon, at every tap

The good news is that TTHMs and the chlorine that creates them are among the most treatable things in your water, and the technology is one Aera builds into every system.

Activated carbon (the whole-home fix)

Activated carbon is the standard, proven technology for reducing chlorine and trihalomethanes. It works by adsorption, the compounds bind to the vast surface area of the carbon as water passes through. Placed at the point of entry, it treats every tap and every shower in the house, which is exactly what this contaminant demands, because the shower is the main exposure route. This is why every Aera system carries activated carbon media as standard. The Signature blends carbon into the tank alongside the softening resin; the flagship Reserve runs a dedicated carbon tank ahead of the resin for the deepest whole-home reduction. Either way, the water reaching your showerhead is dechlorinated, so you are no longer breathing and absorbing what used to be there.

Reverse osmosis (for drinking and cooking)

For the water you drink and cook with, an under-sink RO system adds a final polish, reducing TTHMs along with a broad range of other contaminants at the kitchen tap.

One note for context: a water softener on its own targets hardness, not chlorine or TTHMs. The reduction here comes from the carbon that every Aera system includes, which is precisely why our systems are built to do both jobs at once, soften the whole home and strip the chlorine and its byproducts from every tap.

TTHMs are the clearest reason to think past the drinking glass and treat the water your whole family showers, bathes and breathes in. A free in-home water assessment shows you your actual numbers and what the right whole-home setup looks like for your water.