Formulate as example a problem to determine the flow that can be conducted by gravity from a reservoir to a tank, in a ductile pipe, with loss coefficient of 130 (Hazen-Williams) and a diameter of 20 inches (500 mm). The water level in the reservoir would be 45 meters and the height of the tank where the water is delivered is 25 meters. Total pipe length is 10 km

A video example of a solution using watdis follows (in spanish).