I have to admit that this is important, but it has a visual answer answer as well. My pool contains 135 cubicmetres of water so there will rarely be no water accessable. As long as there is a pale available. I think my Besttank capacity is around 1500 litres. But i have had sometimes problems with the switch starting and stopping the filling of the tank. And you dont see this is defect before the tank allready is empty.