Evaporation is hard to track due to many factors, some of them are, temperature, sunlight exposure, rain, and amounts of rain and light exposure.

Normally a pool, whether it rains or not, will not force one to have to add water within a week’s period. Therefore, if you are adding water more than once a week, there’s a high chance you have a pool leak.

The rule of thumb for water adding would be every 12–15 days when the weather is hot into the 90s and there’s just no rain at all. You also have to account for how much sun the pool gets. If your pool gets sun all day long you could lose about two inches every 5–7 days, but under normal circumstances that the pool gets sunlight partially during the day 12–15 days would be somewhat an estimate of time for one having to add water to the pool.