In particular, the problem of bringing and keeping water on the upper floors is an important constraint in the design of skyscrapers. Water is necessary for tenant use, air conditioning, equipment cooling, and basic firefighting through sprinklers (especially important since ground-based firefighting equipment usually cannot reach higher than a dozen floors or so). It is inefficient, and seldom feasible, for water pumps to send water directly to a height of several hundred meters, so intermediate pumps and water tanks are used. The pumps on each group of mechanical floors act as a relay to the next one up, while the tanks hold water in reserve for normal and emergency use. Usually the pumps have enough power to bypass a level if the pumps there have failed, and send water two levels up.