Hydropneumatic pressure tanks contain compressed air to maintain water pressure in the distribution system so that the need for an elevated tank is eliminated.

As they offer limited storage capacity, they are most often found in systems serving small communities or resorts.

The system generally consists of a tank that can be pressurized, a water pump, and an air pump. Water from the water source is maintained in the lower two-thirds of the tank and air is fed into the upper third of the tank under pressure from the air pump. The system has automated controls to regulate the volumes of air and water in the tank.