Water quality in public swimming pools is a critical public health issue that affects thousands of users across Portugal. Whether in municipal pools, hotels, gyms or sports complexes, ensuring safe and hygienic conditions is an undeniable responsibility for facility managers. Exposure to contaminated water can result in gastrointestinal diseases, dermatological infections and, in more serious cases, transmission of pathogenic microorganisms such as Legionella pneumophila. Therefore, understanding the mandatory parameters, applicable regulations and best management practices is essential for any pool operator.
Mandatory Water Quality Control Parameters
Systematic water quality control is based on well-established physicochemical and microbiological parameters. Free chlorine is perhaps the most well-known: it should be maintained between 0.5 and 1.5 mg/L to effectively eliminate bacteria and viruses, without creating excessive disinfectant levels that cause irritation to swimmers' eyes and respiratory systems.
Water pH is equally crucial. It should be between 7.2 and 7.6, a range that ensures maximum chlorine effectiveness and swimmer comfort. Values outside this interval affect both disinfection and user well-being.
Turbidity measures water clarity. The maximum limit is 0.5 NTU (Nephelometric Turbidity Units), ensuring that the water is crystal clear and any visible contaminant can be detected quickly.
Temperature must be controlled, typically between 24 and 28°C in recreational pools. Beyond comfort considerations, temperature affects the speed of chemical disinfection reactions.
At the microbiological level, testing checks for the presence of total coliforms (which should be absent) and, especially in hot tubs and spa pools, Pseudomonas aeruginosa — an opportunistic bacterium that thrives in warm water.
Legionella Risk in Swimming Pools, Hot Tubs and Spas
Legionella pneumophila is a bacterium that colonises heated water systems. Whilst in conventional pools the risk is reduced due to lower temperatures (20–28°C), it is in hot tubs and spa pools where the danger is genuinely significant. Water temperature (37–40°C), mechanical agitation creating aerosols, and biofilm formation in pipes and jets create ideal conditions for proliferation.
Decree-Law 118/2019, which transposes EU Directive 2016/2318/UE on Legionella into Portuguese legislation, establishes stringent requirements. Facilities with hot tubs and spa pools must implement specific controls, including:
- More frequent disinfection (maintaining free chlorine of 0.5–2 mg/L or equivalent)
- Regular maintenance of piping and components
- Scheduled microbiological testing
- Training programmes for responsible staff
Portuguese Regulation for Swimming Pools
DL 118/2019 is just one part of the regulatory framework. There are specific technical standards for public pools, such as NP EN 15288 (Water Quality in Pools), which detail parameters, testing frequencies and best practices.
The frequency of mandatory testing varies depending on facility type:
- Large pools (>200 m³): testing twice weekly
- Small to medium pools: weekly testing
- Hot tubs and spas: more frequent testing, especially for Legionella
All analytical results, cleaning records and maintenance logs must be archived for a minimum period, facilitating audits and demonstrating regulatory compliance.
Water Quality Management Plan
Effective management requires a systematic control plan. This should include a Legionella Prevention and Control Plan (LPCP) specific to aquatic facilities, which identifies risks, defines operational procedures and establishes responsibilities.
Staff training is indispensable. Operators and managers must understand how to use measurement equipment, interpret results and execute corrective actions when parameters fall outside safe limits.
Daily records of chlorine, pH, temperature and turbidity must be maintained, offering complete traceability. Additionally, a contingency plan must be in place for situations such as disinfection failure, contaminant detection or emergency pool closure.
Conclusion
Guaranteeing safe water in public swimming pools is not merely a legal obligation — it is an investment in community health and well-being. Understanding control parameters, becoming familiar with current regulations (particularly DL 118/2019 and Legionella risks) and implementing a robust management plan are fundamental pillars.
If you operate an aquatic facility and need expert guidance on planning or implementing water quality control systems, we are here to support you. Our experience in environmental compliance and public health ensures that your pool meets the most demanding standards.
Get in touch with us for a free water quality audit of your facility.
