A pond pump is required to maintain proper flow, circulation and aeration of your pond water. Pond pumps are also necessary to keep pond water clean. Pond pumps are available in two options - waterfall pumps (also referred to as aquafall pumps) or submersible pumps. Aquafall pumps imitate the soothing sound and look of a waterfall, whereas submersible pumps function while submerged underwater. Pond pumps are purchased based on the size of your pond and how much water they can pump. Choose a pump that can pump at least half of your pond's water volume per hour. Pumps are measured in GPH (gallons per hour) or GPM (gallons per minute) - according to their pumping capacity. Pond pumps are usually priced between $70 and $380 online.