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Filtering your Water? Don’t Forget the Shower!

A whole home water filtration system is an ideal way to filter all of the water you use, be it for drinking, cooking, laundry, bathing or showering. It might sound like overkill to filter anything but drinking water but filtering your shower water can have unexpected health benefits.

I am going to go as far as to say that filtering shower water is just as, if not more important, than filtering drinking water.

Bold claim right?

Settle in for my explanation. This about a 5 minute read, but if I am already preaching to the choir and you’re onboard for the importance of filtering shower water, check out my top 5 shower filters for 2020.

The first thing to understand about the water you shower and bathe in is that it is normally pre-treated with chemicals such as chlorine to kill potential pathogens. These chemicals do not magically disappear after use and, as such, the water that enters your home can contain residues of chlorine and other disinfection by-products (DBPs).

Chlorine and other gross stuff in shower water

Showering in unfiltered water usually means exposing your body to disinfection by-products (DBPs), typically in the form of chloroform.

Chloroform is a trihalomethane that exists at room temperature as a clear, colorless, heavy liquid with a specific odor you probably recognize from public swimming pools.

Chloroform is the most common trihalomethane in the water supply and is present both in tap water and well water. Swimming pools that rely on chlorination for disinfection also contain trihalomethanes as by-products. Chloroform is light sensitive and degrades in the presence of light and air. The concentration of chloroform is inconsistent in different water systems and in the same system, and trihalomethane concentrations rise as water remains in the distribution system (Ashley et al. 2005).

So, while you might think it’s smart to filter the water you drink (and it probably is smart!), it may make even more sense to prioritize filtering your shower water, given this absorption rate.

Showering and chloroform exposure

The average adult is exposed to 0.199 to 1.89 μg of chloroform per kg of body weight every day, according to the World Health Organization.

Other estimates suggest that exposure could be higher than 3.0 μg/kg of body weight if you account for chloroform inhalation from air and ingestion from food. 1 2

Chloroform is found in food, drinking water, and in the air, but the largest single source of exposure seems to be from showering and bathing.

Daily showering and bathing in unfiltered water increases chloroform exposure both through inhalation and through the skin. This is thought to add 0.36 to 3.4 μg/kg daily, with studies showing increased chloroform concentrations in the blood after using household water for showering, bathing, and even for doing the dishes by hand. 1 2

Specifically, blood chloroform concentrations increased by 2 to 7 times after showering; in one study, water levels of chloroform were 8 and 85 parts per billion, while blood concentrations after showering were 57 and 280 ppt (ng/L). 1

More chloroform absorbed through hot water

One reason why showering and bathing seem to increase chloroform levels so significantly is that you absorb more chloroform through your skin from hot water. At bath-water temperatures of 30°C, volunteers in one study exhaled 0.2 μg of chloroform, versus 7 μg at the highest temperature (40°C). 3

In another study, the absorption of cytotoxic DBPs haloacetonitriles and chloral hydrate (CH) in human skin increased by approximately 50% to 170% when water temperatures increased from 25°C to 40°C. 4

Shockingly, one small study found that swimming for a couple of hours in a chlorinated pool could raise the average concentration of chloroform in breath to as much as 371 μg/m3. 5

Shower water and prenatal health

Worryingly, chloroform and other potential contaminants in shower water, such as benzene, have been shown to pass through the placenta to an unborn fetus where they accumulate at a higher level than in maternal blood. 6

The health effects of unfiltered shower water

Why does it matter how much chloroform and other DBPs are in your water? Well, for a start, higher levels of trihalomethanes have been linked to a higher rate of certain types of cancer, particularly cancer of the urinary bladder and rectum, and possibly colon cancer. 7

Indeed, the US Department of Health and Human Services included concerns over chlorinated water and cancer in the 14th Edition of their Report on Carcinogens, National Toxicology Program.

A 2013 study in South Korea also found a significant association between exposure to trihalomethanes from showering and the lifetime risk of cancer, with up to a 10-fold increase in risk when ingesting shower water. 8

Flint water crisis and DBPs

Concern over DBPs and lead contamination in tap water in Flint, Michigan, made national and international news a few years ago when the city switched its water supply and inadvertently exposed nearly 100,000 residents to potentially unsafe water. Research subsequently revealed that children under 5 who used tap water during this time had much higher levels of lead and DBPs than normal, with potentially life-long consequences for health as well as for their immediate growth and development. Residents were advised to drink filtered water or, in the case of those who were pregnant, to drink bottled water. This advisory seemingly ignored the science showing showering and bathing in unfiltered water to be the greatest source of trihalomethane exposure in the home.

Shower water and skin and hair health

Even before we get to that stage though, unfiltered shower water could be causing ongoing damage to you skin and hair. If your shower water is hard, i.e. if it has a high mineral content, it could leave a residue on your skin and make skin feel dry and irritated. Hard water can also leave hair feeling dry and looking dull, and cause scalp flakiness, thanks to minerals such as calcium, magnesium, silica, and iron. Over time, this may cause hard to break more easily and could increase unwanted frizz. Exposure to chloroform and other DBPs from unfiltered water could also, in theory, reduce your ability to synthesize vitamin D from sunshine. That’s because these DBPs can strip the skin of a variety of natural substances, including cholesterol esters that form previtamin D. 9

Chloroform strips skin of natural oils

Not only does chloroform in shower water strip the skin of its natural oils, reducing the skin’s natural barrier to infection, shower water pipes also appear to have a higher level of bacterial contamination than kitchen tap water pipes, at least according to one study. 10

This may be because less frequent use leads to biofilm formation. Opportunistic pathogens in this water, such as Legionella spp., mycobacteria, Pseudomonas aeruginosa, and free-living amobae (FLA) pose a risk to human health, especially for anybody who is immunocompromised, including young children and seniors. 11

The absorption of some chemicals also increased with the addition of two common surfactants found in shampoos and soaps, sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). 12 Indeed, this same study found that these surfactants (which are also used in car-cleaning products) disrupt the stratum corneum, i.e. the layer of the skin that provides the main barrier protecting us against environmental contaminates. Disruption of the stratum corneum means that the skin has a harder time maintaining moisture levels and keeping pathogens and irritants out. As such, showering in unfiltered water that is hot, while using cleaning products containing SLS or SLES, could have a drying effect on your skin, and may exacerbate skin conditions such as psoriasis and eczema. 

Top health benefits of a shower filter

All in all, installing a complete home water filtration system, or single fixture water filters for your shower and bath water could have benefits including:

  • Reducing skin irritation and dryness
  • Relieving psoriasis and eczema
  • Reducing scalp flakiness
  • Improving hair shine and healthier
  • Reducing frizziness
  • Reducing exposure to opportunistic pathogens
  • Lowering your risk of some cancers.

A shower filter can eliminate or reduce contaminants like chlorine and other DBPs and are relatively inexpensive (especially compared to hair treatments, skin treatments, and medical costs).

They are also super simple to install: unscrew your current shower head, screw in the filter, then screw the shower head into the filter. Easy!

Leigh Matthews

Leigh Matthews, BA Hons, H.Dip. NT, is a health and wellness writer for Gene Food specializing in plant-based nutrition. Read her full bio here.

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