While taking into account the size of the pond, the most important factor to consider is what the pump will do for the pond. Will it power a waterfall? Will it operate a fountainhead or statue? Sometimes a pump is used for recirculation only, with no visible water movement. The way the pump is to be used will determine the size needed.

Waterfalls require the most water flow. To be visually effective, 100 to 200 gallons of water per hour per inch of waterfall width is needed. A waterfall twelve inches wide needs 1200 to 2400 gallons of water flow per hour. More is OK, but less flow means a dribbling falls.

The outlet height is determined by measuring the vertical lift from the pond surface to the height of the top spillway. Add to this one foot for every ten feet of of pipe coming from the pump (which is located as far as possible from the waterfall) to the top spillway. This total outlet height can be matched to the chart for each pump to choose the correct flow rate for your spillways. Be sure to maintain 100 to 200 gallons per inch of spillway at the total outlet height.

Volume is more desirable than pressure in disguising the flow of water into the top spillway. Adapt to larger tubing than the actual outlet size to eliminate pressure while maintaining volume. Determine the length of tubing by measuring the depth of the pond, the distance from the pump that is at the opposite end from the falls, and to the top spillway.