GPH Defined
In pump design, "GPH" means "gallons per hour" and measures how much water the pump will move around each hour without being pumped to any elevation.
Application
Use GPH pumps for indoor tabletop fountains or for larger outdoor fountains and waterfalls, if the manufacturer rates the pump acceptable for outdoor use.
Related Measures
Manufacturers also rate the head or lift of a pump along with the GPH. The maximum head or lift is the highest point the water will reach after the pump circulates it.
Adjustable Models
Some manufacturers will make GPH pumps that the consumer is able to adjust so that it will pump more or less water. This enables users to create specific looks for their fountains at different times.
Size
Purchase a pump that will circulate at least all of the water in the basin once per hour. Look at the GPH rating, as well as the lift rating. You can adjust a slightly larger pump, an undersized pump will not distribute the water properly and at best may only create a surface bubbling effect. Fountain sellers recommend using a 120 GPH pump for a 2-foot high fountain and a 2,000 GPH pump in a 600-gallon basin of water for a 4- to 5-foot high fountain or waterfall.