Drop-off in water level is common in extremely hot areas. To test for pool water loss due to evaporation, get a large ten-gallon bucket and fill it about halfway with pool water. Mark the level of the water in the bucket with duct tape or with a permanent marker and do the same to the level of the water in the pool (Note: do not use a permanent marker on the pool wall, as it will likely not come out.) Place the bucket next to the pool in an area where it will receive the same amount of sun as the pool itself. Turn off your pool pump and keep all swimmers out of the pool for a few days. Three of four days later, check on the level of evaporation of the water in the bucket compared to the level of evaporation in the swimming pool. The amount of water level drop-off should be similar between the bucket and the pool to deem it an evaporation issue, and not a leak. If the pool water level has dropped more, then it is most likely a leak. If it is an evaporation issue, it might be time to invest in a solar pool cover.