A Whole House Water Filter May Improve Your Health

When it comes to water and health, many people are under the impression that all they should do is filter their drinking water. Actually, the tap water you shower and bathe in is just as important because it has contaminants that are readily absorbed through the skin and lungs.[1]

Municipal water departments only clean water up to a certain government standard. Not all contaminants are regulated, and the chlorine that is added as a disinfectant creates chemical byproducts that have been shown to harm humans and animals.[1]

While it's a good thing that these disinfectants protect us from getting infectious diseases, chlorine and its byproducts should be filtered out before use. Fortunately, there are inexpensive whole-house carbon water filters that can remove these chemicals from your water.

Chlorine and its byproducts

Chlorine was first used in the US as a drinking water disinfectant in Jersey City, NJ, in 1908 and quickly spread throughout the country. It helped to eliminate waterborne diseases that once killed thousands a year like cholera and typhoid fever.[2] Thankfully, in most developed countries, chlorine has virtually eliminated those problems – but it may come with a cost.

In 1974, it was discovered that when chlorine dissolves in water it reacts with naturally occurring organic matter to create what are known as disinfection byproducts (DBPs). This discovery led to research on other chemicals formed when chlorine is added to water, and more than 600 water disinfection byproducts have been identified.[1]

DBPs form when chlorine reacts with natural organic matter in water. Only a few of those, trihalomethanes (THMs) and haloacetic acids (HAAs), are regulated and are used as an indicator for all potentially harmful compounds in your water.

Trihalomethanes (THMs or TTHM)

There are four primary trihalomethanes: chloroform, bromodichloromethane, dibromochloromethane, bromoform.[1]

Both chloroform and bromodichloromethane have been classified as possible human carcinogens by the International Agency for Research on Cancer (IARC). In studies of animals exposed to THMs, these chemicals have been shown to cause liver damage, liver toxicity, and kidney tumors.[1]

THM levels increase over time if the water is not used and also increase as temperatures rise, so the highest levels are generally found during the summer in the parts of the distribution system farthest from the water treatment plants.

Haloacetic acids (HAAs or HAA5)

The five primary haloacetic acids are known as HAA5: monochloroacetic, trichloroacetic, dichloroacetic, monobromoacetic, and dibromoacetic acid.

HAAs may be carcinogenic and have been associated with reproductive and developmental effects in laboratory animals. The current regulatory levels set for HAA5 is because of concern that exposure to HAAs over many years may increase the risk of cancer.[3]

It's not just about drinking water

Humans are exposed to disinfection byproducts (DBPs) through drinking water and oral, skin, and inhalation of chlorinated water. For people who take hot showers or baths, inhalation and skin absorption accounts for more exposure to DBPs than drinking water.[1][4]

Inhalation during showers

I don't know about you, but I've never thought about inhaling my tap water. Yet whenever you take a shower a fine mist of water vapor particles are created and inhaled into your lungs.

The EPA estimates that inhalation can contribute greater than 10 percent of the ingestion dose of certain DBPs during a shower.[5] For chloroform it's been found that inhalation is roughly equal to skin exposure in a shower.[6]

Skin absorption

Our skin is the largest organ in our body, and it readily absorbs chemicals from what it encounters, whether that be beauty products, lotions, oils, or just plain old water.

Through a process known as dermal absorption, chemicals in water are transported from the outer surface of the skin into the bloodstream. This process is aided by hot water that makes the pores of the skin open up.

According to one study, certain chemicals enter the body at a significantly higher rate through the skin than through the digestive system. For example, bromodichloromethane, a chlorine byproduct associated with adverse birth outcomes, absorbs through the skin at a rate of 62%, yet by drinking the same water only 27% of the substance would get into the body.[7]

Health risks of disinfection byproducts

Due to the large population exposed, health risks associated with disinfection byproducts (DBPs), even if small, need to be taken seriously. Byproducts, if consumed in excess of EPA's standard over many years, may increase health risks.[8]

The EPA has therefore acknowledged that public health is improved by reducing exposure to DBPs. Some disinfectants and DBPs have been shown to cause cancer and reproductive effects in lab animals and suggested bladder cancer and reproductive effects in humans.[9]


  • Cancer and birth defects in animals – Chlorine disinfection byproducts have been shown to cause liver damage, liver toxicity, kidney tumors, and birth defects in animals.[1][10]
  • Microbiome and cancer – Chlorinated water alters gut bacteria in mice and may be a cause of colorectal cancer.[11]
  • Asthma in children – Use of indoor chlorinated pools by children less than 6-7 years of age appears to promote the development of asthma.[12]
  • Birth defects in humans – Drinking chlorinated water while pregnant may increase the risk of having children with heart problems, cleft palate, and major brain defects.[13][14]
  • Bladder cancer in men – A meta-analysis indicates that long term consumption of chlorinated drinking water is associated with bladder cancer, particularly in men.[15]

Lesser of two evils

The US Environmental Protection Agency (EPA) has developed rules that attempt to find a balance between the risks of waterborne pathogens and those of disinfectant byproducts.[10] Disinfection byproducts are not regulated individually, instead there is only a standard for total levels of THMs and HAAs.

The way the EPA, Centers for Disease Control (CDC), and municipal water departments talk about chlorine is as a necessary evil, to eliminate the greater risk of waterborne illness.

Waterborne pathogens pose a real and more immediate threat to health; water disinfection byproducts are certainly the lesser of these two evils – CDC[1]

What else is in your water?

City water can contain many pollutants, such as heavy metals from the pipes, bacteria that wasn’t killed by the chlorine, viruses, various chemicals that made their way into the water reservoir from where the city water is taken, pesticides, nitrates and so on.

Not all contaminants are regulated by the government. The EPA regularly evaluates substances that may be in public water and works with local water departments to help determine where contaminants occur and whether they need to be regulated.[16]

As of 2016, many different pharmaceuticals, industrial chemicals, and synthetic hormones are known to occur in public water systems.[17]

  • Pharmaceuticals – Many different pharmaceutical drugs end up in the water supply and aren't typically removed. These include synthetic hormones found in birth control pills and hormone replacement therapy.[17][18][19]
  • Pesticides – Many different insecticides, herbicides, and fungicides are known to occur in public water.[17]
  • Industrial chemicals – Chemicals used in industrial applications, such as solvents, antifreeze, refrigerants, and others end up in our water supply.[17]
  • Heavy metals – Metals such as arsenic, cadmium, barium, copper, lead, or mercury enter the water supply through industrial and human waste, pipe erosion, or because of acidic rains that break down the soil and contaminate groundwater. Metals are particularly toxic for the human body and can cause irreversible brain damage in children.[20][21]
  • Fluoride – Fluoride is naturally found in soil, food, and drinking water, but is also added to city water supplies, toothpaste, and other products. The reason for doing so is that fluoride fights tooth decay. However, too much of a good thing is also problematic. Excess fluoride intake leads to dental fluorosis (white spots on the teeth), pain and damage to bones and joints, thyroid problems, neurological problems, and even impaired development in children.[22]

Final thoughts

Up to 60% of the human body is composed of water, and we need to drink over half a gallon of water each day, on average, to stay well-hydrated and healthy.[23] The quality of the water we drink is vital to our general state of well-being, but also the water we use in our showers and baths.

Many people take it for granted that the water they bathe in is safe – but the truth is that local governments make tradeoffs when it comes to the costs and risks of waterborne pathogens versus the long-term effects of disinfection byproducts.

These tradeoffs are different than what some health-conscious individuals, parents, and pet owners would make. If you can afford it, consider filtering all your water before use. Read about my experience buying an affordable whole-house water filter.