"The devil of the water garden is algae," says landscape designer John Knox. "It's always good to have running water." Of course, that's not the main reason Knox and fellow designer Sisso Doyle like to get the water moving in the gardens they design. There's the business of oxygenation, or aeration, which enhances water clarity and contributes to fishes' well-being. There's the mesmerizing beauty of a waterfall. And there's the gurgle of rushing water--in Doyle's view, "one of the most charming aspects of the garden."
It's possible to have an algae-free pond without a pump or filter, says Knox, but it is much more difficult to attain the balance of plant life that's required to achieve it. A submersible pump pulls water from the oxygen-depleted area near the bottom of a pond and drives it through a spouting statue, into a fountain, or to the beginning of a waterfall. A mechanical or biological filter keeps the water clear by removing algae, fish food, and waste. (Biological filters cost at least twice as much as mechanical ones but just half as much to operate, and they don't need cleaning as often.) Although not essential, a filter is a good idea if you plan to keep fish. A low-voltage pump is economical and easy to install.
If you're designing a waterfall, keep it in proportion to the pool below. Consider its width and height and how much water flow you want. That will determine, in part, the size pump you need. A liner beneath the course of the fall eliminates the heaving and cracking that old rock and masonry models endured.
The most important thing, says Knox, is to make the waterfall appear as natural as possible. "We always strive to come up with a fall whose source of water is not apparent," he says. "When it emerges from between a couple of positioned rocks, you have the sense that the water flows naturally from an outcropping."
The best waterfall, perhaps, leaves you free to wonder. Even if you built it yourself.
