The filter system is considered the heart of the pool. It consists of a filtration pump which circulates the water in the filtration circuit; and a filter which purifies and clarifies the water by retaining all the impurities. Without filtration, the water degrades and stagnates, so it is essential to choose and size your pool filtration properly. To preserve the quality of your water, the filtration cycle must allow all the water in the basin to pass through the filter in less than six hours, four being the optimum. Thus, for a rectangular swimming pool with a volume of 40 m3, the minimum flow rate of your pump should be 10 m3/h. However, it is preferable to increase this figure by a factor of 1.2 to 1.5 to take into account various factors that could hinder the circulation of water.