Why the pre-swim shower isn't just about hygiene
There's a sign in almost every public pool in Europe. It's often faded, sometimes ignored, and almost always poorly explained: “Shower before entering the water.” Most people read it as a rule of good manners, or at most collective hygiene. Few know that behind it lies a precise technical reason, one that directly affects water chemistry, the stability of the lining, and its lifespan.
What a bather who hasn't showered brings into the water
The human body is a continuous source of organic compounds. Sweat, sunscreen residue, cosmetic oils, skin oils, traces of urine — all of this enters the pool with the bather. The most chemically critical components are nitrogen-based: urea, ammonia, amino acids, creatinine.
Urea is the main issue. It's estimated that the average adult carries up to 50–80 mg of organic nitrogen on their skin per swim if they haven't showered. Multiplied by the number of bathers, it's easy to see how the organic load in a public facility can quickly become significant — and how even a private pool, if used regularly, isn't immune either.
A 60-second shower removes the vast majority of these compounds before they reach the pool. It's not a symbolic gesture: it's a real chemical barrier.
Chlorine isn't an unlimited incinerator: what chloramines are
Chlorine acts as an oxidant: it attacks organic molecules and breaks them down. But this reaction has a cost — it consumes available free chlorine and produces disinfection by-products, the best known of which are chloramines (monochloramine, dichloramine). Chloramines form exactly from the reaction between chlorine and nitrogen compounds. They're responsible for the sharp smell many people mistakenly associate with “too much chlorine” — in reality it's the opposite signal: there's too little free chlorine and too much organic pollution to manage.
The consequences on the lining: mineral deposits and biofilm
When the disinfection system is struggling, the consequences also show up on the lining. The first effect is deposits of metals and carbonates: calcium, magnesium and iron dissolved in the water tend to precipitate preferentially on surfaces where an organic layer is present, resulting in greyish-white or brownish stains, often mistaken for “dirt” but actually mineral deposits encrusted on the lining.
The second effect concerns bacterial adhesion and biofilm: without effective oxidation, bacteria find favourable conditions, form biofilm and produce metabolites that worsen surface deterioration. Field diagnostics have found bacterial colonies located exactly in the zones of greatest exposure — the waterline and the walls near the skimmers. That's no coincidence.
pH and temperature: the two variables that make everything worse
Beyond what's been said so far, two other variables make the picture worse in a non-linear way once the bacterial load rises: pH and temperature amplify everything.
An acidic pH (below 7.0) increases the solubility of pollutants, creating more aggressive conditions for all materials in contact with the water. Many private pools tend toward a low pH, believing it “makes chlorine work better” — a mistaken choice that carries a long-term cost, both chemically and on the lining.
High temperature (above 30–32°C) accelerates all the chemical and biological processes described. A heated pool with poor chloramine management is exactly the worst condition for the longevity of the whole system, as well as a favourable environment for bacterial growth.
The real cost of an ignored habit: what the warranty says
A quality PVC-P lining represents roughly a third of a pool's total cost — it's not the cheapest item in the project. Early replacement due to accelerated chemical degradation, although rare, isn't covered by warranty, because water management is the responsibility of the facility operator.
Best practices: shower, pH and combined chlorine under control
Mandatory showering, correct pH management (7.2–7.4), monitoring of chloramines (combined chlorine < 0.6 mg/L according to European guidelines) and adequate filtration are the tools that protect the investment. Simple, inexpensive tools that are systematically underestimated.
This isn't bureaucracy. It's basic chemistry applied to everyday actions. Bathers who haven't showered bring an organic and bacterial load into the pool that puts pressure on the disinfection system. Oils, fats and nitrogen compounds bind to dissolved minerals, settle on surfaces, alter the lining and trigger the processes that produce stains and degradation often blamed on “poor-quality products” or installation errors. The pre-swim shower is the first line of defence — inexpensive, immediate, with a direct impact on the lifespan of the system.
“A minute under the water before entering the pool can extend the life of the lining, reduce chemical consumption and help the whole system run better.”
Samuele Petrini, Technical Manager ALKORPLAN Renolit Italy