There are many pumps suitable for powering fountain and/or waterfalland choice will depend on the number and scale of the effects desired.
Pumps are divided into two categories, submersible pumps and surface pumps, both powered by electricity.
Surface pumps are those which are installed outside the pool. They draw water from the pool via a strainer and a suction pipe, and then deliver it to the fountain or waterfall outlets through polythene tubing. Half-inch diameter tubing is adequate for delivery to fountains or fountain ornaments; delivery to waterfalls may be in 1, H or even 2-in. Internal diameter tubing, depending on the volume of water required to achieve the desired effect.
A surface pump must be housed in a dry, ventilated brick-lined pump chamber, carefully sited to ensure that both suction and delivery lines are kept as short and as straight as possible in order to minimise friction loss. The chamber must be large enough to accommodate the gatevalves which control the flow to each delivery line, as well as the pump itself. The pump chamber floor should have ahole to a soakaway beneath to avoid any danger of flooding. A cover to the chamber is necessary but a waterproof lining should not be attempted: the result will be heavy condensation inside and eventual damage to the pump. The chamber may be successfully camouflaged in a variety of ways: I have seen one in a flight of shallow steps, one of which was the chamber lid; one an apparent tree stump; and others in the guise of seats and ornament pedestals.
Surface pumps tend to be more audible than sub-mersibles and they do need more plumbing and the construction of a chamber. But they are certainly cheaper than submersibles of comparable output, and for any scheme involving a combination of several fountains and waterfalls a surface pump offers considerable economies.
Submersible pumps are those designed to operate completely under water, so there is no need for pipework from pool to pump and back, or for a pump chamber. A submersible pump simply sits in the pool sucking in water through a strainer and pushing it up through a fountain jet (often fixed directly on to the pump) or through tubing to the head of a waterfall. Some submersibles are capable of supplying both a fountain and a waterfall simultaneously, but if several outlets are required the greater capacity of a surface pump may well be needed.
If you have ambitious plans in this direction do not hesitate to take advantage of the services offered by specialist water garden suppliers. Given all the details of what you want to achieve, and particularly the vertical lift and horizontal delivery distances involved and the sill width of the waterfall, they will not only advise you about the best pump and the necessary bits and pieces, but will probably be able to offer you a comprehensive kit for the job, complete down to the last hose clip.
For small to medium-sized pools requiring no more than a fountain and/or a waterfall there is no doubt that a submersible pump kit will be ideal. It will, at that level, be less costly than a surface pump, far easier to install, and silent in operation. It will be provided with a length of waterproof cable sealed into the unit, sufficiently long to reach out to a convenient spot near the pool where connection is made through a weatherproof connector to whatever length of additional cable is necessary to run back, suitably protected, to the nearest undercover 3-pin electricity outlet.
Siting the Pump
When a pump supplies a waterfall a fair volume of water will be sucked out by the pump at one point and poured back into the pool from the waterfall at another. There is a widely held notion that these points should be at opposite ends of the pool to create a stream between them. This is quite wrong: currents must be kept to the minimum. The shorter the distance between the exit and entry points, the better it will be in every way. The pump (or strainer in the case of a surface pump) must be positioned as close to the waterfall as possible, thus reducing water movement to the smallest possible area.
One impractical idea which seems to be very popular is to have a fountain in a small upper pool supplied by water pumped from the main pool; the water from the fountain spray is supposed to overfill the top pool and then pour as a waterfall down into the main pool. It won’t work; it can’t work because the volume of water that comes through a fountain jet is tiny compared with the volume needed to make even a modest waterfall. The water from the upper pool just wouldn’t pour, it would dribble. If you really want this sort of effect it could be achieved by using two pumps, one small submei-sible sitting in the upper pool producing a fountain, and a second sitting in the lower pool piping enough water to the top pool to make a decent waterfall. I am only saying, mind you, that it is possible, not necessarily that it is a good idea!