Unless you're a contractor, installing a waterfall may seem like a huge undertaking. But pond equipment suppliers have gone to extraordinary lengths to help even first-timers succeed.

They offer packaged kits, complete with instruction manuals, videos that describe the installation, and filters, pumps, and pond liners. Or you can buy individual parts to piece together.

Your water garden can be a tiny tuck-in, or a large one with many falls. But before installing a large water feature yourself, learn all you can about the process and the equipment options.

Take a class (offered by some pond suppliers), and peruse books such as Garden Pools, Fountains & Waterfalls (Sunset Publishing, Menlo Park, 2001; $14.95; 800/526-5111).

For design ideas, check out other water gardens in your neighborhood. Many pond suppliers sponsor tours of residential water gardens early each summer to benefit charities; for details, ask your pond supplier about Parade of Ponds. Other factors to consider are the following.

THE SOURCE. In nature, waterfalls come from somewhere―a meandering stream that disappears into the woods, for instance. To avoid the "spilling from the wall" look and to create the illusion of a waterfall's source, angle the falls and flank them with boulders or plants.

PUMP. Before you buy a pump, you'll need to know how many gallons of water your pond will hold and the height of your waterfall. Here's why: Industry standards call for all of a pond's water to be recirculated every two hours. Pumps are rated in gallons per hour (gph), but in practice this rating declines for every foot the pump has to lift the water. Most pumps come with a chart that lists gph for each of several discharge heights (called "head height"). To calculate the number of gallons of water your pond will hold, multiply its volume in cubic feet by 7.48.

ROCKS. Rocks are often sold in "head" sizes (as in the size of a person's head). For most ponds, one- and two-head rocks work best. Blend different colors; in a pond we built in our test garden, we mixed white cobbles with blue ones and brought in some large boulders for accents (all from Graniterock; 831/471-3400). Remember that big rocks can be heavy. Some suppliers will deliver and position them for an hourly fee (in advance of delivery, plan where you want them to go). If there are naturally occurring rocks on your site, try to include some of them.

FISH. Koi are beautiful and easy to keep. To protect them from raccoons and herons, provide enough plants to cover at least two-thirds of the water's surface; plants will also create hiding places among rocks. If marauders still come after them, switch to less expensive goldfish. For protection, some people stretch bird netting or a fan of clear fishing line over their garden pond.

COST. Pond/waterfall combinations range in price from about $500 for a preformed pond shell to $25,000 or more. Choose the right system for your budget.