Shade isn't just good for keeping evaporation down - its also vital for your fish. So many folks are making water gardens these days - but they are mostly not deep enough so the water heats up much more quickly - especially if there is little or no shade. I reckon more garden fish die of broiling than any other ailment.
Hey Clancy, good point BUT water plants still need about 5-6 hours a day of full sun, so don’t make it too shady. The ideal would be to have shade from the scorching afternoon sun. Dappled shade is very good for the afternoons as light levels remain high without the scorch.
If you are starting a new water garden then make sure its around 60-70cms in depth unless you live in a very cold area in which case it should be deeper. Then the larger in area it can be the better as this will help to keep a more stable overall water temperature.
If its too small or too shallow then the sunlight will accelerate algae and bactieria growth.