Very small amount of water:
 Due to the small amount of water there is a high concentration of dirt in the water. If 3 prople go into the whirlpool the load is the same as if 150 people go into an 8 x 4 m swimming pool.

Very high water temperature:
 A whirlpool is operated with 35 to 38 degrees warem water. This is the ideal temperature for bacterie. At these temperatures, one bacterum can become 1 billion bacteria in 10 hours only.

A strong swirling of the water:
 Due to the strong turbulence of the water, the carbon dioxide in the water gasses out and lime precipitation can occur. The turbulence also causes many disinfectants (such as chlorine) to be broken down more quickly.

Very many pipelines:
 A whirlpool with 50 jets can have up to 100 m of piping with 150 square meters of inner surface. Limestone, fats, cosmetics, bacteria with biofilm can settle there. Many pipelines such as the air pipes cannot be flushed through.

Very small filter systems in the whirlpool:
 Compared to the pollution of the water, the filter systems are undersized and the filter running times are very often much too short. This means that the dirt remains in the whirlpool and must be cleaned chemically.

• Lime and carbon dioxide are always in the water
• They are chemically bound together and dissolved in water
• A lot of carbon dioxide + a lot of lime in the water = hard water
• Through the heating and turbulence of the water: carbon dioxide is emitted and the dissolved lime is transformed into limestone: Limestone settles in the inner walls of the pipes. A whirlpool with 50 jets has approx. 100 m of pipes with approx. 150 m2 inner surface. These can be completely covered with limestone. Thus bacteria find a hold and fats settle. The bacteria multiply and form a biofilm. 

• They originate from the skin and get into the water despite previous showering.
• They form thousands of the smallest invisible drops in the water.
• These drops get stuck on rough surfaces and accumulate there.
• At the interface of the drops, between oil and water, bacteria accumulate.
• The bacteria use the oils as a food source and form a biofilm.
• Oils and cosmetics are very difficult to oxidize with disinfectants: high dosages are necessary

• Biofilms are a survival strategy of bacteria.
• They settle down and produce a mucus of polysaccharides.
• The biofilm protects the bacteria from disinfectants such as chlorine.
• Biofilms are formed in the pipelines, on free-floating oil drops, in the filters.
• 95% to 99% of the bacteria live in the biofilm. Only 1% to 5% of the bacteria in the whirlpool can be killed with classic disinfectants.
• Biofilms grow permanently and develop very quickly.