The pump is the heart of a pond with a waterfall or fountain. Too small, and the waterfall is a trickle; too large, and it splashes water out and wastes electricity. This calculator finds the flow you need and the head the pump must overcome.
Flow for a waterfall
The look of a waterfall depends on how much water passes over each inch of spillway width. Common rules of thumb:
- about 100 gallons per hour (gph) per inch for a light trickle;
- about 150 gph per inch for a medium sheet of water;
- about 200 gph per inch or more for a heavy, loud flow.
A 12 in spillway with a medium sheet needs 12 × 150 = 1,800 gph.
Total head
A pump’s flow drops as it pushes water higher and through longer tubing. Manufacturers publish a pump curve that shows the flow at each head. The total head is roughly:
total head = vertical lift + 1 ft for every 10 ft of tubing
The lift is measured from the pond’s surface to the top of the waterfall. With a 4 ft lift and 20 ft of tubing: 4 + 2 = 6 ft. Choose a pump that delivers 1,800 gph at 6 ft of head, not one rated at 1,800 gph with no lift, which would fall short.
Each elbow, valve and the filter adds a little more resistance; wider tubing reduces it. Use tubing at least as wide as the pump outlet, often 1½ in or more for this flow.
Pond turnover
For clear, healthy water, most pond builders aim to circulate the whole volume at least once every 1 to 2 hours, and once an hour for ponds with fish. A 1,000 gallon pond with 1,800 gph turns over 1.8 times an hour.
Running cost
Pond pumps usually run day and night:
yearly cost = watts × 8,760 hours ÷ 1,000 × price per kWh
A 150 W pump at $0.17 per kWh costs about $223 a year. Energy-efficient pumps with permanent magnet or variable speed motors use much less for the same flow, and a smaller pump on a timer can run a fountain only when you enjoy it.
Tips
- Place the pump in a skimmer or on a raised block to keep it from sucking up debris.
- Use a GFCI-protected outdoor outlet.
- Check the pump curve and choose a pump that runs near the middle of its range, not at its maximum head.