Pumps are like the heart of the garden. They are the devices that push water through filters, up through fountains, and along streams. They vary widely in size, power, and price. You can purchase a tiny pump for a container water garden for just $10 or $20. A larger pump that will move water through a 50-100 gallon water garden (about the size of a large bath tub or deep wading pool) will cost about double that. Still larger pumps for bigger water features, or water features that need to propel a lot of water into a tall fountain or up a hill can cost as much as a few hundred dollars.
Small pumps that operate in a tiny water garden, without fish or plants, usually don’t need filters. But other pumps, sitting in the bottom of a pond, and dealing with leaves, fish waste, and water garden plant parts, need to have a filter to prevent them from clogging. This is sometimes called a pre-filter. (Other types of filters play a role in keeping the water healthy and clear.)
Some pumps have their pre-filters built right in. It’s usually made of the same black plastic as the pump case and has a series of slots (called the strainer cover). That strainer cover also usually snaps off for easy cleaning under a hose or faucet.
The key number to look for when shopping for a pump is GPH—gallons per hour. That’s how many gallons the pump can move every 60 minutes. Choose a pump that will be able to move 100 percent of the total volume of your water garden in one hour. So if a pond holds 250 gallons of water, the pump must move at least 250 gallons per hour. When in doubt, it’s smart to buy more GPH rather than less. Most pumps allow you to adjust downward the flow, to get just the effect you want.
Pumps also have an outlet. Depending on your design, this can be fitted with a fountain head to pump the water directly upward. Or it can be fitted with tubing that run alongside the pool to a waterfall to move water up so that it can then cascade downward and back into the pond and through the pump once again.
How to Calculate GPH
To determine how powerful a pump you need (how many GPH) you’ll need to first figure the volume of your water garden. You can find online calculators, or you can do a rough estimate yourself. First measure the volume of the pond or pool by taking some simple measurements. If it’s an oval or abstract shape, measure it, in feet, at its longest point, its widest point, and its deepest point. Then calculate the volume you would for a rectangular shaped pond. With a stream, measure it in the same way. This method will give you more gallons than the actual amount, but that’s okay, because your pump should powerful enough to turn over at least the total volume of water every hour.
Once you’ve figured how many cubic feet you have, convert the cubic feet into gallons by multiplying that number by 7.48. If you are creating a waterfall of any height, or will have extensive tubing running from the pump, or your waterfall will be very wide, you’ll need additional GPH. The easiest way to figure out the additional GPH is to look at the pump packaging information. Quality pumps will provide information on power needed for various heights and for varying feet of tubing. If your waterfall is wide, use this general rule: For a 1-inch deep sheet of water 1 inch wide over a waterfall, add 150 GPH. So for 1 inch of water flowing 6 inches across, you’d need to add 900 GPH to achieve that.
Fountains
Fountains are powered by the water pushing out of pumps. The most popular types of fountains fit onto special valves coming out of the pump. They are made of black plastic and snap on easily. Different fountain heads allow you to choose different water patterns—a simple bubbler, a dome, a tiered spray, and more. The fountain head often is on an extendable black tube that slides up or down to achieve the desired height. Or you may want to purchase yet more tubing to make the fountain higher. In a pond, you can also adjust height by setting the pump on top of stacked stone or bricks, or even a black plastic milk crate, set upside down. More powerful fountains attach separately to the pumps with additional tubing. With smaller fountains, like the type in container gardens or in free-standing tiered fountains, the pump is built right into the fountain.
