Tips for correct watercourse calculation - use the pump performance curve to identify the required pump capacity. To deliver the desired water quantity from the pump to the source of the watercourse minimum hose diameters are required e.g. up to 20 l/min = 25 mm (1”) or from 50 l/min 38 mm (1 1/2”) etc. Pay attention to the pressure loss of the water supply line; this is also important for the watercourse. Generally this is considered with 0.4 mWc. Consequently, for displacement of greater quantities of water it is necessary to use a more powerful filter & watercourse pump. Larger water quantities increase pipe friction loss, and a higher capacity pump is required. Here is a rule of thumb for determining the right pump for a watercourse: Watercourse width in cm x 1.5 l/min. = capacity in l/min.