There are two types of water pumps: centrifugal pumps and positive displacement pumps. Centrifugal pumps use a rotating impeller to create flow, while positive displacement pumps displace a certain amount of water with each stroke.
The main difference between an impeller and a water pump is that an impeller is a type of rotor used to increase the pressure and flow of fluid, while a water pump is a device that moves fluids by mechanical action. Impellers are commonly found in centrifugal pumps, while water pumps can be either piston-type or diaphragm-type.