All living creatures, including your aquarium fish, need oxygen to live. An aquarium water pump helps to create enough oxygen to keep the fish and plants in your aquarium healthy. Gases, including oxygen, dissolve in water. The surface area of the water determines the rate at which the gas dissolves. An aquarium water pump agitates the water increasing the surface area, which creates pressure in the water to keep it moving. The pump draws air through a one-way inlet valve before ejecting it into the water via the outlet. This creates bubbles in the water.