How often does the water need to be changed?

With an outdoor pool, you do not need to change the water at all, because it renews itself completely within 1.5 years purely through rainwater: A 4x8 meter pool holds 37,500 liters of water, and with average annual rainfall in Germany, 25,000 liters of rainwater are added to the pool per year. In 1.5 years, the pool's volume is completely renewed once. It is also assumed that pools no longer get as dirty in winter as they did years ago, when roller shutter covers and winter leaf nets were not yet common. Therefore, at the start of the season, only a fraction of the maintenance is required, and as described above, the water simply remains in the pool forever.

With an indoor pool, this is naturally somewhat different: Here, fresh water must be continuously supplied, if only to compensate for evaporation. The water should be changed completely once every three to five years, because the chloride content in the water also increases over time.