A sheet of plastic floating in the surface while you don't use it could help to reduce the evaporation. If is a big pool put some holes here and there to allow air access if somebody or a pet falls into the pool.

Some marginal plants strategically placed and Nymphaeas can shadow the water (reduce the amount of heat that reaches the water), but you would have a very different kind of pool then and they have their own maintenance issues.

If your area allows the culture of columnar cactus and succulents, use it near the pool to provide shadow. They will rarely trow anything into the water and may be beautiful to see by itself. Look for the less vicious species like Euphorbia or Pilosocereus azureus that are strongly vertical while young, refreshing to see (blue is blue) and will not pose any problem if cultured in a wooden raised bed. The idea would be to make a short wall using the cactus as logs placed a few dm apart to allow the wind passing trough. You will need to avoid the access to cats protecting the dirt with a mesh, aizoaceae, gravel or rocks. Allow a lot of space for the roots. A small pot will not really work.

Cactus or succulents allowed to grow on the roof or near the house will act also as fire retardants (but not fire supressors) as they accumulate water.