Various impurities enter the water, and they are removed during filtration. The filter can be filled with a sand or glass bed. The filter works with a special suction and force pump that takes water from the pool. The impurities remain on the bed, and clean and fresh water returns to the pool. The filter must be cleaned during the rinsing process (backwashing) – the bed is raised and mixed so that the dirt can be separated from the grains of the bed and all impurities flow out through the pipe at the top of the filter. The entire rinsing process takes up to 5 minutes. It is very important to choose the right size of the pump and filter-adequate to the size of the pool. The capacity of the pool should be filtered at least 3 times per 24 hours, assuming the pump works 16 hours.