A pressure tank as part of a home's water system has multiple purposes. It stores water and provides water under pressure when the pump is not running. It builds up a reserve supply of water so the pump starts and stops less often, prolonging the life of the pump. A pressure tank is important because it keeps water pressure at a constant level. It also keeps the water and air separated. Without these features the water pump would turn on and off quickly – a problem caused cycling – which can quickly burn out the pump motor.