Bacteria, algae and other organisms thrive under warm water conditions this is obviously harmful not just for athletes but the general public in a commercial swimming pool, for competitive/ training pools the water should be no higher than 28°C, for recreational pools the recommended maximum is 29°C
Olympic swimming, Red Cross & FINA (The international governing body of swimming, diving, water polo, synchronized swimming and open water diving), have set the water temperature for competitive swimming between 25°-28°C. Warmer water is less dense and therefore less friction as a swimmer’s body moves through it. Standard water temperatures ensure that all performances are on a level state of conditions.
Most hotels and resorts worldwide keep the temperature of their pools at a comfortable 27° to 29°C. This is warm enough for comfortable swimming and lounging. Same for most residential estates, institutional and public pools.