There are two main categories of water pumps, submersible and surface mounted. Submersible pumps are installed under the water while surface pumps are mounted out of the water. Submersibles are usually installed below the water level in a well but can be installed in a lake, cistern or river. Surface pumps are usually mounted above the water level which requires a suction lift, the distance between the water level and the inlet of the pump. However if a water storage tank is used the water level could be above the pump creating a positive suction head.