Water you can drink with confidence and a pool whose air does not sting the eyes are two things an advanced guest checks in silence.

Why it matters

In the room, they look at where the water they are offered comes from: plastic bottle, tap, carafe. At the poolside, they notice the so-called "chlorine" smell and often know that it is not the smell of chlorine. They ask for nothing. They compare.

Both subjects can be addressed with few resources, and above all with information on display.

What science establishes

The pool smell comes from chloramines. Chlorine disinfects the water, then reacts with what bathers bring in: sweat, urine, cosmetics. Disinfection by-products form, including trichloramine, an irritant gas that passes from the water into the air of an indoor pool. Teo et al., 2015; Yang et al., 2018. Established.

More swimmers, more trichloramine in the air. Measured continuously in an aquatic centre during a competition, airborne trichloramine rose with the number of swimmers. It was highest just above the water, where swimmers breathe. Wu et al., 2021. Established, at a single site.

Beyond a certain level, the airways react. In a Belgian municipal pool where trichloramine repeatedly exceeded the value of 0.5 mg/m3 (reference value cited by Seys et al., 2015), 22 of the 26 swimmers and coaches tested showed bronchial hyperresponsiveness. The cause was a glue used to repair a pipe. Seys et al., 2015. Among staff at Swedish pools, eye and nose symptoms are more frequent; at the low levels measured, no effect on lung function was found. Löfstedt et al., 2016. Established, in regular swimmers and staff, not in hotel guests aged 55 and over.

The benefits of swimming outweigh the known chemical risks. This is the conclusion of a review of the available epidemiology, which recommends reducing these risks rather than avoiding the pool. Villanueva and Font-Ribera, 2012. Established.

What is emerging

Biological markers shift after a session. In 49 non-smoking adults who swam for 40 minutes in a chlorinated indoor pool, trihalomethanes in exhaled air increased sevenfold, and some markers of genotoxicity varied with exposure. Kogevinas et al., 2010. The authors conclude that by-products should be reduced, not that swimming should be given up. Emerging.

Plastic from bottles. A recent imaging method counted about 240,000 plastic particles per litre of bottled water, 90 % of them nanoplastics, far more than was previously measured. Qian et al., 2024. The study covers a few brands, in a single laboratory. What these particles do in the body is not established. Emerging.

What we refuse to say

We do not say that tap water in a European country is dangerous. Where it meets the standards, it is monitored, and the WHO guidelines for drinking water set the framework.

We do not say that filtered, alkaline, "structured" or enriched water improves health. None of these promises is supported.

We do not say that a chlorinated pool is toxic, nor that a "salt" pool is chlorine-free: salt electrolysis produces precisely chlorine.

We do not say that nanoplastics in bottled water cause disease. We say that a hotel can offer filtered water in a reusable container, which removes the question.

What a hotel can do

Why the subject is neglected. Water in the room is often treated as a minibar product, and the pool as a technical item. The guest sees in them a signal of care.

Minimum baseline (around a few tens of euros per room). A filter jug, or a glass bottle filled at a filtered water fountain on each floor; the origin of the water and the type of filter stated on a card. For the pool: daily display of the treatment method, free chlorine, combined chlorine and pH, already recorded for regulatory purposes; a shower before bathing that is genuinely encouraged, because less brought in by bathers means fewer chloramines.

Optimised baseline (around a few thousand to a few tens of thousands of euros, depending on the pool). A filtered water fountain on each floor with logged maintenance. For an indoor pool, verified ventilation, with air extraction close to the water surface, and a complementary treatment such as activated carbon, described in the technical literature for lowering by-products. Teo et al., 2015.

The target. Filtered water available in the room without single-use plastic, and a pool whose values are published every day. The orders of magnitude are indicative, to be confirmed by quotation.

What the Living Lab measures

Measurement planned. The Living Lab, near Lisbon, is being equipped in waves. Measurements will cover tap water before and after filtration (free chlorine, hardness, dry residue) and, in audited venues with a pool, the displayed values of free and combined chlorine compared with an independent reading.

The results will be published here, dated.

Sources

• Teo TLL et al. Chemical contaminants in swimming pools: occurrence, implications and control. Environ Int, 2015. doi:10.1016/j.envint.2014.11.012
• Yang L et al. Regulation, formation, exposure, and treatment of disinfection by-products (DBPs) in swimming pool waters: a critical review. Environ Int, 2018. doi:10.1016/j.envint.2018.10.024
• Wu T et al. Real-time measurements of gas-phase trichloramine (NCl3) in an indoor aquatic center. Environ Sci Technol, 2021. doi:10.1021/acs.est.0c07413
• Seys SF et al. An outbreak of swimming-pool related respiratory symptoms: an elusive source of trichloramine in a municipal indoor swimming pool. Int J Hyg Environ Health, 2015. doi:10.1016/j.ijheh.2015.03.001
• Löfstedt H et al. Respiratory and ocular symptoms among employees at Swedish indoor swimming pools. J Occup Environ Med, 2016. doi:10.1097/JOM.0000000000000883
• Villanueva CM, Font-Ribera L. Health impact of disinfection by-products in swimming pools. Ann Ist Super Sanita, 2012. doi:10.4415/ANN_12_04_06
• Kogevinas M et al. Genotoxic effects in swimmers exposed to disinfection by-products in indoor swimming pools. Environ Health Perspect, 2010. doi:10.1289/ehp.1001959
• Qian N et al. Rapid single-particle chemical imaging of nanoplastics by SRS microscopy. PNAS, 2024. doi:10.1073/pnas.2300582121
• Organisation mondiale de la santé. Guidelines for drinking-water quality, 4e édition incorporant les premier et deuxième addenda, 2022. who.int
• Organisation mondiale de la santé. Guidelines for safe recreational water environments, volume 2 : Swimming pools and similar environments, 2006. who.int

Also from the founder

Question 15 · What is measured in the place itself: air, light, water?

The longevity audit for venues  ·  The Research Journal

IO8 Living Lab, near Lisbon. Measured, never promised.

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