Evaporation rates depend on a number of factors including the surface area of the pool, ambient temperature, exposure to direct sunlight and relative humidity. Evaporation rates of between 2% to 5% per week are considered average. An easy way to test if a pool is leaking is to set a bucket on the first step and fill the bucket with water until the water inside the bucket is equal to the pool water on the outside. Several days later, check to see it the water levels are still equal. If so, the water loss you have been experiencing is just evaporation. If the water level in the pool is lower than the water level in the bucket then you may have a leak.