The best site for a water garden is on level ground and in a spot where you can see and hear it from the house, patio, or garden bench. It should be within reach of electric power (plan to have an electrician wire it for you). Make it deep enough for plants and fish―18 to 24 inches in most regions. Though local codes sometimes vary, national codes require fencing for any pond more than 2 feet deep.

Waterfall
Terraced soil or stacked stones provide a place for the water to spill over. New waterfall boxes combine a waterfall and biological filter in a single box.

Pond plants
They work with filters and fish to reduce algae. They also consume carbon dioxide, which helps keep water clear. You can grow a wide array of plants in and near the water. Just keep them clear of the splash from the waterfall.

Marginal plants, such as cannas, flowering rush, Japanese iris, and papyrus, grow in boggy soil at pond's edge or very shallow water (underwater shelves give you a place to set these plants).

Deep-water plants rest at least 18 inches below the surface (2 feet is common), but their leaves and flowers float on the surface. One beautiful example is parrot's feather (Myriophyllum aquaticum), a lacy-foliaged plant. Water lilies (Nymphaea) add a lovely splash of color when they bloom in warm weather. Choose from hardy varieties or exotically colored tropicals (in cold climates, bring them into a greenhouse or sunroom during winter).

Free-floating plants, such as water lettuce (Pistia), dangle their roots in the water, from which they take up nutrients.

Gravel
It fills spaces between rocks. For a natural look, use two sizes (3/8-inch and 5/8-inch); mix them in a wheelbarrow.

Rocks
Choose ones that are angular enough to be stackable but rounded enough that they won't poke holes in your liner.

Beach
Include a shallow, gravelly section accented with larger stones. Birds love it!

Pump and filters
Pumps recirculate water in a garden pool and deliver it to the head of a waterfall. Filters trap small debris and help keep the water clean.

Liner
The best kind is a flexible, UV-resistant material such as 45-mil EPDM rubber, which is fish-safe, patchable, and warranted for 20 years or longer.

Plant shelf
This is a ledge for potted plants. Generally, make it 1 foot below the waterline and at least 1 foot wide, although it can vary based on plants' needs.

Fish
They dine on mosquito larvae and help keep the pond water balanced and clean. A rule of thumb: Stock your pond with 1 inch of fish for every square foot of water surface. Add them three or four days after the pond is filled with water.

Underlayment
This is a sheet of woven plastic padding. It helps protect the liner from punctures by rocks or other sharp objects in the soil beneath the pond.