GARDEN without water is something I never understood, and even when I was obliged to live in a rented house it was possible to have a horse trough with some goldfish and a water lily.

In Washington, which has agreeable warm summers with not many terrible nights dipping down to the 60s, water lilies and pool fish thrive - though in our bad winters the fish may die if not protected.

Ideally, a garden ought to have a lily pool as roomy as possible - mine is 10 by 12 feet - and not to split hairs about it, it should be of concrete poured into wooden forms, all at once.

Observation over the years suggests to me that fountains, filters, underwater lights, painted walls and bottoms, and tile linings are all a great waste of effort. The best lily pool is one of unadorned concrete under the water. It is silly to have filters since the water is naturally clear in wellmanaged lily pool, and as for paint and tiles, they do not show up under water since the surface acts as a mirror.

The pool should be 24 inches deep, and the concrete walls 6 inches thick. There are books at libraries about actual construction. I would not myself build a pool of stone, brick, cinder block or twigs (somebody must have tried twigs by now), but I have heard they sometimes work well. The number of joints, however, seems to me an invitation to disaster and leaks.

The pool should be in full sun or, at the least, with 3 1/2 hours of direct sun upon it.

Common goldfish, the sort sold as fish bait, are as decorative as any. This spring they were 20 for $1 at my neighborhood pet shop.

I am a great believer in anacharis or elodea, usually called "seaweed" by landlubbers. It grows in streams in this part of the country. I got my start from a stream near Great Falls. Books say you get awful parasities this way. I did not.

A surface of 100 square feet of water (a pool with a surface 10 feet by 10 feet) will accommodate 100 goldfish, and 25 or 30 will be plenty. The gardener sooner or later learns that there is no special magic in maximums. Of course if you are wild about fish, you could safely have 100 6-inch goldfish. Very small goldfish, just turned gold, will reach 3 or 4 inches the first summer in an uncrowded pool.

There are two sorts of water lilies: the hardies, which die down in the winter and return every spring forever, and the tropicals, which you set out at the end of May and allow to perish in the winter, starting with new plants the next year.

Among the hardy water lilies, admirable kinds are "James Brydon," a rosy red sometimes with a silvery look on the exterior, and "Chromatella," with a soft primrose-to-sulfur color. Both are free-blooming, well-behaved and for all practical purposes flawless. Ironically, they are among the oldest - 19th century - varieties in commerce.

I have tried numerous others. Some grow very large and need space, while others are not so free-blooming as the two mentioned. But all are desirable, and I mention these only because they are superb' for gardeners who do not want to survey the whole field and who want the best varieties.

Among tropical water lilies, "Pennsylvania" or "Blue Beauty" (it goes under both names) is wonderful, so is Gen. Pershing," a pink, and "Emily Grant Hutchings," a rich smoldering red with a touch of magenta that blooms at night. There are dozens of others - I always liked the nearly navyblue "Director George T. Moore," for instance - and any one would give pleasure.

In a pool of 100 square feet, I would use "Marliac Pigmy," a delightful miniature flower the size of silver dollars or very small pancakes, a sort of ivory-primrose color; and the two I mentioned first; plus "Pennsylvania." That, with plenty of seaweed and 25 goldfish would be enough. The water would be sufficiently shaded by lily pads to remain clear, but enough surface would show to reflect the sky and the landscape nearby.

But suppose there is not room for a pool that large.

Then build a smaller one - 4 by 6 feet is a nice size. Or suppose even that is too large? Then a 4-or 5-foot metal tank, circular, could be set flat on the ground and walled up with just one course of bricks and mortar, or mortar set with tiles, etc.

Once I gave directions for a half-barrel water garden, and many wrote to say it had given them enormous pleasure. Others complained they never could get the whisky out of the barrel and it killed fish and never worked out right.

I allow my hound to trot around on the ice of the pool in the winter and do not forbid her drinking out of it and peering at the goldfish. I also would not object to her swimming in it, if she were into swimming. But people are kept out of the pool, not that many have tried to get in it.

Water lilies have tuberous roots that are planted in a plastic tub filled with good heavy garden loam without chemicals in it. The tub is set on the concrete floor of the pool, so about a foot or 18 inches of water covers the top of the dirt.

Once I warned a friend (who was keen to cover the bottom of his pool with a foot of dirt, instead of using tubs) not to do that, but of course he did anyway. He later had to dig it all out. There is nothing fatal about spreading earth on the bottom (God does it in ponds) but it is harder to control plants, find car keys and other dropped objects, and in brief it is a bad idea.

In my experience it is important to have fish, water lilies covering about a half or a third of the surface, and plenty of elodea, otherwise scum forms. If you follow directions, however, you will have no scum, no mosquitoes and no murky water.

There are ready-made fiber glass pools, and the only thing wrong with them is they are not usually 24 inches deep, as I like, but they work quite well. I also dislike the shapes of most of them, and I strongly object to seeing the rim, which should be covered with a coping.

Pools look best full to the brim. Some people, who err, think they look better with a couple of inches between the water level and the coping. Keep it at the level you prefer. For me, any pool is ruined if there are any signs of pumps, plastic liners, and the like.

What is wanted is a sensible serviceable masonry tank. If I used a vinyl liner (which saves all the cost of masonry and is therefore tempting), I would be careful to have the rim of it completely concealed.