Introduction
A well-maintained pool is a sanitarily safe environment. A badly maintained pool is a medium in which microorganisms pass from one person to another through the water — and the mechanism is always the same: insufficient disinfectant, or disinfectant made ineffective by the wrong pH.
This article describes the transmission routes, the four groups of problems that show up in practice, and how each is prevented. It is not a clinical diagnosis article: symptoms after using a pool are a matter for a doctor. It is an article about what in the water allows that to happen.
Important note: the recommendations here are about maintenance and use. For any health question, consult your doctor or SNS 24 (808 24 24 24).
The Four Transmission Routes
| Route | How it happens | Risk group |
|---|---|---|
| Swallowing water | Swallowing water while swimming | Children, above all |
| Skin contact | Wet surfaces, water, coping | Everyone |
| Inhaling aerosols | Fine droplets, especially from jets and in enclosed spaces | People with respiratory problems |
| Mucosal contact | Eyes and ears | Everyone |
The swallowing route is the most relevant for children, because they swallow more water. The skin route is the most frequent overall. The inhalation route is the least common, but it is the one associated with more serious illness where poorly maintained hot water or hydromassage equipment is involved.
The Four Groups of Problems
1. Gastrointestinal
How they are transmitted: by swallowing water contaminated with material of faecal origin, even in minimal, invisible quantities.
Risk context: disinfectant missing or very low, a faecal incident in the water — more likely with small children — or a user with a gastrointestinal illness in progress.
The point worth knowing: some microorganisms relevant to this group are notably chlorine-resistant and can survive a considerable time in water disinfected under normal conditions. This has two practical consequences:
- A faecal incident is not resolved with a usual chlorine dose. It requires the pool closed, an enhanced treatment and prolonged filtration.
- Anyone with diarrhoea does not get in the water. Not that day, and not in the days that follow. It is the only genuinely effective measure against this group, and it depends entirely on users' behaviour.
2. Skin
Folliculitis ("hot tub rash"): a rash of small papules, typically in the areas covered by swimwear, appearing hours after bathing. It is associated above all with hot water with insufficient disinfection, where the temperature degrades the disinfectant faster.
Fungal infections and plantar warts: these are transmitted by wet surfaces, not by treated water — coping, showers, changing rooms, mats. Flip-flops and not walking barefoot in wet communal areas is the prevention that works.
Irritant dermatitis: not infectious. It results from out-of-range pH or from chloramines, and is worse in people with sensitive skin. See Pool for People with Allergies.
3. Ears
Otitis externa ("swimmer's ear"): inflammation of the ear canal, favoured by moisture retained in the canal and by water with insufficient disinfection. It is one of the most frequent problems among people who swim a lot.
Practical prevention: tilt the head and dry the ears well after swimming, do not use cotton buds — which remove the natural protection and can make things worse — and keep the water in condition. Anyone with repeated episodes should talk to their doctor about what to do in their case.
4. Respiratory
Chloramine irritation: coughing, sore throat, worsening asthma. It is not an infection: it is chemical irritation from combined compounds, and it is worse in indoor spaces with insufficient ventilation. See Water Quality and Health.
Aerosol-associated infections: the relevant risk scenario is hot water equipment — hot tubs, hydromassage, spas — with deficient disinfection and pipework where water stagnates. The combination of warm temperature, stagnation and missing disinfectant is what creates the problem; the production of fine droplets is what carries it.
Practical consequence: hydromassage equipment requires more rigorous maintenance than a pool, not less. If it has been unused for a while, it does not get switched on without treating the pipework.
💡 Dica Profissional
The most reliable indicator of a pool's sanitary risk is not the chlorine figure: it is the **pH plus free disinfectant pair**. With high pH, a perfectly acceptable chlorine reading corresponds to weak disinfection. If you can only control one parameter rigorously, control pH — it is what makes the disinfectant work.
What Actually Prevents
In order of effectiveness:
1. Free disinfectant always present, with pH in the appropriate range. This is the basis of everything. Without it, none of the other measures compensates.
2. Filtration sufficient for the volume. It removes particles and organic matter that consume disinfectant and can harbour microorganisms. No product replaces filtration.
3. Shower before getting in. It drastically reduces the organic load introduced, which preserves free disinfectant and reduces chloramines.
4. Do not get in the water with a gastrointestinal illness. The most effective measure against the group of problems hardest to treat chemically.
5. Proper swim nappies, changed away from the pool area.
6. Do not walk barefoot on wet communal surfaces. It prevents fungal infections and plantar warts, which do not come from the water.
7. Dry the ears well after swimming.
8. A written record of the parameters. It does not prevent directly, but it is what lets you catch deviations before they become problems. A water-analysis log template solves the format.
Signs That a Pool Should Not Be Used
Valid for any pool — at home, at a hotel, in a condominium or in a rental:
- Cloudy water. If you cannot see the bottom, you do not get in. It is simultaneously a sanitary risk and a safety risk.
- A strong, persistent smell. It indicates chloramines and a high organic load.
- Slippery surfaces or biofilm on the walls and at the waterline.
- Coping with green or brownish deposits.
- No treatment record, in a collective-use pool — the most informative sign of all, because it means nothing is being measured.
Common Mistakes
Trusting the smell. A pool that smells of chlorine is not a disinfected pool — usually the opposite.
Measuring chlorine and ignoring pH. It is measuring half and concluding double.
Treating a faecal incident with a normal dose. It is not enough. It requires the pool closed, enhanced treatment and prolonged filtration.
Getting in the water with diarrhoea. It is the behaviour that generates most pool-associated gastrointestinal outbreaks.
Switching on a hot tub that has stood unused for months. The pipework has to be treated first.
Compensating for filtration with chemicals. It does not work, and it masks the problem.
Assuming a hotel pool is treated. The visible signs above apply anywhere.
Frequently Asked Questions
Does chlorine kill everything?
Not with the same ease. Some microorganisms are far more resistant than others and can survive a considerable time in normally disinfected water. That is why behavioural prevention — not getting in with a gastrointestinal illness, showering before getting in — is indispensable and cannot be replaced by any product.
Can I swim with an ear infection?
That is a question for your doctor. As a general principle, you do not get in the water with an active ear infection.
Do you catch fungal infections from pool water?
Practically never. You catch them on the wet surfaces around it — coping, showers, changing rooms. Flip-flops remove most of the risk.
Is a saltwater pool lower risk?
It disinfects on the same principle, generating chlorine from salt. If the pH is out of range or the cell is not producing, the risk is exactly the same. See Saltwater Pool Maintenance.
What do I do if there is a faecal incident in the pool?
Get everyone out of the water, remove the material, and carry out an enhanced treatment with prolonged filtration before reopening. It is not a situation to resolve with a routine dose.
In a condominium pool, what can I ask to see?
The treatment record with the readings and the dates. It is the document that shows whether the pool is being measured or merely cleaned. See the condominium pages.
Conclusion
Health problems associated with pools do not come from the water: they come from the absence of effective disinfectant, and what makes disinfectant effective is pH.
Key points to remember:
- The critical pair is pH plus free disinfectant. Measuring chlorine without pH tells you nothing.
- Some microorganisms are chlorine-resistant — behavioural prevention is indispensable.
- Anyone with diarrhoea does not get in the water. The most effective measure in this article.
- Fungal infections come from the wet surfaces around the pool, not from treated water.
- Hot water and hydromassage require more rigorous maintenance, not less.
- Cloudy water, strong smell and no record: do not use the pool.
- For any symptom, talk to your doctor or SNS 24 (808 24 24 24).
If you want to know the sanitary state of your pool water, the on-site technical diagnosis measures pH, free and total disinfectant, and assesses filtration and circulation, with a written report. It costs €45, deductible from your first month under contract.
