Water chestnuts, once available only canned in this country, are now for sale fresh. For anyone who has tried only canned water chestnuts or has never had them at all, the fresh are a wonderful surprise. They have a sweet crispness reminiscent of coconut meat and are as refreshing as spring water.

Giant's Someplace Special and Georgetown Safeway carry the fresh, while other Giant and Safeway supermarkets will order them when requested. Given the availability of fresh water chestnuts, it would be disappointing if American cooks didn't figure out ways to use them. Chopped or sliced, their sweet crunch could complement the richness of custards or creamy desserts. They're delicious sliced or halved with soft-fleshed fruit or berries, and they're good eaten plain.

Water chestnuts, which do resemble chestnuts with the addition of a small tufted point, are corms (underwater stem tips) from which a kind of water grass sprouts. Cultivated throughout China, they're a favorite of the ducks that paddle around the streams and ponds where they grow.

Like most ancient Chinese foodstuffs, they were originally valued as medicine. Water chestnuts are cooling and are thought to sweeten one's breath. A paste made from the starchy powder of dried water chestnuts is fed to children who accidentally swallow coins or other metallic objects. This same powder -- available in Chinese groceries -- is an excellent substitute for cornstarch; it gives sauces a pleasing sheen and produces extra-crisp fried foods when used in a batter.

To peel water chestnuts, first rinse them of any mud. Cut off the flat top and bottom skin, then simply pare the circular edge with a small knife. You may keep them briefly in cold water until ready to use. An occasional water chestnut turns up fermented with a taste like sweet wine; it's not unpleasant or harmful, but you may not want to use it. Discard any whose white flesh is discolored or moldy.

Pick over water chestnuts individually, choosing only those that are rock-hard. The freshest have a slight sheen. If you can't find them fresh, the canned variety will do only for a cooked dish where water chestnuts are a minor feature.

WATERCRESS AND WATER CHESTNUT SALAD (4 servings)

This recipe, adapted from Time-Life's "The Cooking of China," is easy to make and may be prepared ahead. Its sharp fresh taste complements a rich main course.

4 bunches watercress

10 fresh water chestnuts, peeled and chopped finely

1 teaspoon light soy sauce

1 tablespoon sesame oil

1/2 teaspoon salt

1/2 teaspoon sugar

Start a large pot of water to boil. Meanwhile trim and discard any large stems of the watercress. When the water comes to a boil, drop in the watercress, stir it briefly, then immediately drain it, and run it under cold water to stop the cooking. Squeeze the watercress with your hands to get rid of most of its liquid, then chop it finely and put in a mixing bowl with the chopped water chestnuts. Combine the remaining ingredients, and add to the bowl. Toss and serve.