My plumbing textbook states that doubling a (water) pump's capacity results in a fourfold increase in head. Can you lead me to an equation that would express this relationship. An example is used in the same text: "a pump that operates at 3500 rpm can pump twice the capacity of a pump that operates at 1750 rpm, but the 3500 rpm pump generates four times the head of the 1750 rpm pump." I looked for an answer but couldn't find one.