How fast will the water evaporate in an above ground pool?

It depends on whether the pool is considered "enclosed" inside a pool house or not. The assumption in such case is that the pool house prevents "outside" air circulation which enables the humidity inside that "house" to be maintained at a high level which minimizes evaporation. It goes without saying then that if you keep the doors to your pool house open then you loose much of the evaporative benefit of having the pool enclosed. In any case, high ambient outside air temperature will increase the pool evaporation rate but an enclosure should slow it down. Pool covers can also decrease evaporation rate. More input from FAQ Farmers: * Go to Arizona edu. There you will see a contour map of the U.S. providing annual evaporation rates in inches of loss per year. Find the rate for your area. Divide the rate by 365 to get the daily rate in inches of loss per day. * If you are concerned of a leak place a bucket of water on the steps of the pool and fill it so that the level equals the pool(u might have to weigh the bucket down with a rock or something) check the level the next day to see if they both evaporated the same.