It’s a long time since I mentioned this subject but we do need to talk about this. Really. Do you shower before swimming in an (indoor)? If not, why not? Do you pee in the pool? In two UK and US studies, 1 in 5 adults admitted they have and in the UK study 70% don’t shower beforehand. Amongst general swimmers we can be certain the peeing figure is much higher whereas with elite swimmers the figure is almost 100%.

I was reading a swimming forum discussion about this subject, which asked the number of people who showered before swimming. No firm percentage was gathered but it was the majority who didn’t clean before a swim. Many swimmers admitted to never showering beforehand. Some said entire swim squads never showered and their coaches never enforced the rule. It was both interesting and disquieting with the general lack of misunderstanding about the essential role of pre-swim showering for everyone.

An example: Even when we have dry land training first and are quite sweaty my whole team just jumps in the pool. Doesn’t bother me.

No evidence of any awareness by swimmers or coach there.

That was in fact the most popular comment. It was repeatedly indicated that showering before using the pool was less common in the US than many other countries. I can’t put hard figures on that though since the forum is populated predominantly by American swimmers. Showering before using the pool is common (but nowhere near universal) behaviour in Irish pools. But only yesterday I was doing a 10k swim and twice during it I could taste perfume and deodorant in the water after two different people entered at different times. Even lifeguards don’t all know the reasons why showering is important.

A small minority of people did say it was courtesy to other pool users to shower before swimming. A not-quite-as-small amount indicated that more people not showering required more work by the pool to balance the chemical load to get the filtration system to work properly/optimally, particularly having to increase chlorine.

Both these items are true but secondary to the main issue.

First you have to ask yourself; why is chlorine added to water? You all know: to kill communicable pathogens (particularly bacterial or parasitic). But it doesn’t kill everything. Cryptosporidium, which many have heard about from news stories of infected municipal and domestic water supplies, can live for days in chlorine.

Sweat, soap, perfume, shampoo, conditioner, aftershave, deodorant, urine, faeces are all organic compounds which contain proteins.

When organic compounds are introduced into a chlorinated (or brominated) environment like a swimming pool, disinfected by-products are produced. While the chlorine is intended to neutralise harmful pathogens specifically from faeces (urine is sterile) it also has undesirable side effects.

Chlorine reacts with the organics to create gases whose family are called Trihalomethanes (THMs). It reacts with proteins to form Chloramines which include Nitrogen Trichloride.

Trihalomethanes are colourless odourless heavy toxic gases. Chloramines are nitrogen chloride gases which display the strong chlorine smell people associated with the smell of chlorine in pools (and not actually indicative of such) and also toxic.

The extent of these gases produced is a function of the amount of organic matter entering the water: The more organic matter the greater the gaseous concentration AND a subsequent prerequisite increase in the amount of chlorine that must be added to the pool to keep it balanced.

Chlorine in any form is toxic. It impacts respiratory function and some THMs are carcinogenic. At the highest THM concentrations in pools in a study the cancer risk was deemed to be unacceptable (Study link 5 below). Asthma is more prevalent amongst competitive swimmers:

The risk of asthma is especially increased among competitive swimmers, of which 36% to 79% show bronchial hyperresponsiveness to methacholine or histamine (1).

THMs lie in a thin layer on the water just where most commonly you and I are breathing, which is how people absorb the majority of them. About a third is also absorbed through skin, and some by swallowing. There’s no way of avoiding them if they are present.

The more organics brought into, or urinated into the pool, the worse the health situation. A greater chlorine smell in a pool hall means the worse the pool chemical balance, not cleaner water.

By now you hopefully understand if you didn’t already:

You should be showering before entering a pool. Regardless of if you have showered already that day.

You should be showering after using a sauna before entering a pool.

You should not be peeing in the pool.

If your pool doesn’t encourage showering, why not write a simple letter to them explaining that by doing so they reduce their chemical costs (by up to 50%).

If your friends and fellow pool users don’t do so, your example and encouragement is even more important.

Related articles

(1) Allergy and asthma in elite summer sport athletes. (PubMed)

Distribution and determinants of trihalomethane concentrations in indoor swimming pools.

Nitrates, chlorates and trihalomethanes in swimming pool water. (American Journal of Public Health).

Pathways of trihalomethane uptake in swimming pools (Science Direct).

(5) Cancer risk assessment from exposure to trihalomethanes in tap water and swimming pool water (Science Direct)

Drowning in Disinfection Byproducts? Assessing Swimming Pool Water (Environmental Science & Technology)