A hot tub is not a small pool. The water is warm, there are many bathers per litre and the bubbles create aerosols that people breathe in. That is why the rules treat hydromassage more strictly, mainly because of two bacteria: Legionella and Pseudomonas.
Why hydromassage is different
Between 30 and 40 °C bacteria grow much faster than in a cold pool, disinfectant is used up sooner, and sweat and lotions build up in a small volume of water. The jets also create aerosols: tiny droplets that are breathed in. That is how Legionella reaches the lungs.
The legal limits
Spain's Royal Decree 742/2013 (annex I) sets, for the pools it applies to:
- Pseudomonas aeruginosa: 0 CFU per 100 ml.
- Legionella spp.: under 100 CFU per litre in heated pools with jets or aerosols.
- Temperature of the hydromassage tub: 36 °C maximum.
In the Madrid region, Decree 99/2024 explicitly extends its scope to hydromassage tubs, keeps the 36 °C maximum and requires a heated tub to be closed if the water goes above 40 °C.
The numbers set by the rules
The cleaning required against Legionella
Royal Decree 487/2022, on legionellosis prevention, distinguishes two cases:
- No recirculation (filled and emptied): water changed after each use, daily cleaning and disinfection.
- With recirculation: residual disinfectant always present, monthly checks and full cleaning and disinfection every 6 months.
What about the hot tub at home? RD 487/2022 excludes buildings used exclusively as homes, unless they affect the outside (and the health authority may still require measures). Not being required does not mean there is no risk: the same care protects your family.
A sensible spa routine
- Test chlorine or bromine and pH before each use, not once a week.
- Shower before getting in: fewer lotions, less disinfectant used.
- Clean or replace the filter cartridge according to use; that is where biofilm hides.
- If the water smells strong, foams or is cloudy, do not use it until it is corrected.
- Keep the spa covered when not in use and fully drain and disinfect it regularly.
Frequently asked questions
What is the maximum hot tub temperature in Madrid?
In facilities covered by the rules, the hydromassage tub must not exceed 36 °C, and Decree 99/2024 requires a heated tub to be closed if the water goes above 40 °C.
How much Legionella is allowed in a spa?
RD 742/2013 sets under 100 CFU per litre of Legionella spp. in heated pools with jets or aerosols, and 0 CFU per 100 ml of Pseudomonas aeruginosa.
How often must a hot tub be disinfected?
Under RD 487/2022: without recirculation, water changed after each use and daily cleaning; with recirculation, continuous residual disinfectant, monthly checks and full cleaning and disinfection every 6 months.