Backfill the gap between the reservoir and the sides of the hole with soil and firm it in to make sure that the reservoir is stable. Make a catchment area by sloping the surrounding soil slightly towards the rim of the reservoir. Place two bricks at the bottom in the reservoir to act as a plinth for the water pump, then position the pump.
Make sure that the pipe you use for the fountain spout is 5-8 cm higher than the sides of the reservoir. Line the catchment area with a plastic sheet. You can cut it so the plastic drapes into the reservoir or you can cut a hole in the center for the fountain pipe. Fill the reservoir with water.
Check that the water pump is working then position the plastic sheet over reservoir with the fountain pipe protruding through the hole. Fit the fountain spout. Weigh down the edges of the plastic sheet to keep it in place as you work.
Place a piece of heavy-duty galvanized mesh on top of the plastic sheet to support the weight of the large cobbles you are going to put over. Make sure the mesh is large enough to rest on the rim of the reservoir. Place a finer mesh on top of the larger one to prevent smaller stones to fall through.
Cover the area around the pump with a layer of cobbles. Check to see if the height of the spout is satisfactory and when you are happy with the fountain finish it by arranging the cobbles so that the spout is hidden.