GARDENING : WATER GARDEN A COOL NOVELTY.

Byline: Joshua Siskin

The Garden of Eden had a river running through it, and ever since, nearly all famous gardens have had water features.

The first formal gardens, planted in ancient Egypt 3,500 years ago, were arranged in straight lines along irrigation channels. An oasis garden, which must contain some kind of water hole if not an actual pool, is a practical solution to life in dry climates like our own.

When the weather is hot, there is no saving grace such as a water garden. Actually, no matter what the weather, a water feature will transform virtually any garden into more of a garden - that is, more of a refuge from the outside world - than it otherwise would be.

Roughly speaking, there are two kinds of water features: moving, running, sound-producing water features (streams, fountains, waterfalls) and standing, quiet water features (ponds and pools).

For dramatic effect, nothing can match the movement of water. Its sound pulls you magnetically into the garden. You don't have to build a Grand Coulee Dam to produce the desired result; submersible pumps are inexpensive units that create all the splash and gurgle you need. They are effective in any water feature, whether on level or inclined terrain.

A water pond need only be 20 inches deep. It can be any size or shape and should be moderately sloped on the sides. Plastic liners are what most experts recommend for holding the water; they are easy to install and relatively inexpensive. You can put such a liner in a whiskey barrel on the balcony or in any Olympic-size excavation in the backyard.

It is not recommended to plant a water garden in the shade. Flowering water plants are sun lovers, and they require at least six daily hours of unobstructed light to strut their petals. When a tree is allowed to grow up over a water garden, not only is light stolen from the aquatic plants, but tree roots may grow through the pond liner, causing leakage. Remove leaves from the pond surface immediately. When leaves settle on the bottom of a pond, they remove oxygen and encourage the growth of algae.

Water liners are everyone's favorite pond plants. The hardy lilies are most popular; they disappear into dormancy in winter but come back each spring. Their flower colors are yellow, pink, red or white. Tropical water lilies, which are killed in most Valley winters, are famous for their blue and violet colors during warm weather. Water lilies do not open up on overcast days.

A balanced water pond requires little maintenance. Ponds become clogged with algae from the presence of too many fish or decomposing leaves - both of which provide nitrates for algae growth - or insufficient plant coverage. Algae is sun-loving and so, as a further measure to prevent algae's proliferation, see that 60 percent of the pond surface is covered with the foliage of your favorite aquatic plants. In the enormous water pond at the Japanese Garden in the Sepulveda Basin, just north of Burbank Boulevard in Woodley Park, there are few water plants, but the algae cannot get a foothold due to the telapia fish that feed on them.

A concise, illustrated book called ``Water Gardens'' (Firefly Books; $10.95) has just been published. It offers a good introduction to the subjects of pond construction and maintenance, water gardening in containers and water plant selection. The September-October issue of Organic Gardening features water gardens and how they benefit the environment.

I am interested in visiting unusual gardens in Los Angeles and writing about them in these pages. I would also enjoy witnessing examples of horticultural prowess. Daily News readers who wish to show off their plants are invited to write or send an e-mail to me and we'll feature some of them here.

MEMO: Joshua Siskin's column appears every Saturday. He welcomes questions from readers. Write to him in care of the Daily News Features Department, P.O. Box 4200, Woodland Hills, Calif. 91365-4200. You can also reach him through this on-line mailbox: JoshSiskinaol.com.