my landscape architect designed an infinity edge spa that can't be covered and is trying to convince me to go with an uncovered spa. We mainly want a cover to retain heat and conserve water and energy.

He says that the water is circulated from the pool anyway, so a cover won't help with heat retention. Is that really the case? How much more evaporation would one get from an uncovered infinity edge pool than a regular covered in-ground spa?

I don't want to take his word and later discover that we are wasting a lot of water and energy to maintain this spa and should have just covered it.