Siting the pool
Water gardens, except bog areas, which can stand a certain amount of shade, are best situated in an open, sunny position, otherwise the water tends to green up with algae. If you are using a fountain or similar, place the pool where you are most likely to get the benefit from the sound of splashing water, otherwise an informal pool is sometimes better in a peaceful spot away from the house.
Never install a pond where it can fill up easily with leaves — for example, near deciduous trees or shrubs. This might look picturesque, but debris dropping off the branches soon rots and fouls the water, and can be fatal to fish. Always make the pool as big as you can manage it in proportion to the rest of the area.
Constructing your pool
There are many materials which can be used for holding water, some better than others:
Naturally moist areas
A few people are lucky enough to have a part of the garden which is always wet, either because of springs, seepage, or a stream. In this case, if the bottom is dug out, water will usually stand in it, although the natural level might be lower than that in an artificial pond, but the banks can be planted up with suitable pondside plants to very good effect. If the site is soggy, but does not contain standing water, it can be used for growing bog-loving subjects in a similar manner to a herbaceous border.
Once this was about the only reliable method of making a pool. As it requires a lot of heavy work to get it right and there are other problems concerning possible leaking and contamination of the water with salts out of the new concrete, it is not a method to be recommended nowadays for the amateur gardener with so many other materials at his or her fingertips.
Another outdated method sometimes used in localities where a lot of heavy clay was freely available. Basically, it consisted of ramming wet clay and sometimes straw into the hole until it was so solid the water could not drain out. Apart from the sheer physical effort involved, this method had its drawbacks in that if the water level was allowed to drop and the sides dried out, they would probably crack and the pond would start to leak. There are other methods more suitable.
Heavy duty polythene sheet is available from water gardening suppliers. This is used, often as a double thickness, to line the hole before filling it with water. Its main advantage is the reasonable cost, but it punctures easily if the hole is not completely free of sharp stones, and deteriorates rapidly in sunlight, so the lining needs renewing after a year or two.
Semi-rigid plastic shapes
These are made, usually in a neutral shade, of stiff but flexible plastic and simulate a rough, informal pool bottom. The hole is dug out to fit the plastic shape and then soil is rammed in around the sides at the same time as the pond is filled. They are reasonably priced but, not being entirely rigid, if not installed properly, once the pool starts filling with water, the pressure will push it out of shape and it can collapse and distort in all directions.
Fibreglass and plastic preformed pools
These are quite expensive but available in a whole range of sizes and shapes to suit every requirement. They are usually stone-coloured but some are made in a garish blue or very light colours which look totally unnatural and do nothing for any landscape. They can be obtained with imitation stone edging or plain edged for covering with your own material — crazy paving or grass, for example. They are much easier to install once the hole is there than the semi-rigid sort, but the base must be smooth, level and firm before the preformed pool is finally placed. The levels in each direction should be meticulously checked before backfilling and running water into the pool. They should incorporate a shelf for marginal plants.
These are probably the easiest to use, although good ones are expensive. However, unlike polythene, they do not deteriorate in sunlight so should last for many years provided that they are installed correctly in the first place, that you do not tread in them, and that you do not stick a fork through the bottom. These days they are usually made from PVC, nylon-reinforced PVC or butyl, the latter a very expensive material, but being of toughened rubber material, very strong. PVC sheets are usually coloured grey or blue, sometimes one colour on one side and one on the other, while butyl is an unobtrusive charcoal grey.