Will the rate of pool water loss decline as level goes down?

Yes. There are two basic factors that determine the rate of evaporation: temperature and surface area. Because a pool loses water through evaporation in the same way as any lake, the hotter the air, the faster the water evaporates. The second key factor in evaporation is the amount of surface water exposed to the air. Surface water is the only water from which molecules are capable of lifting into the air as vapor, so the more pool surface area there is, the more evaporation will occur. As the level of the water in a pool goes down, the surface area of the pool available for evaporation also decreases so less vapor will be released.