How to determine if your swimming pool is leaking or not
To identify if your pool has a leak, you need to know if its rate of water loss is greater than the evaporation rate.
Sure, you could have splashout from swimmers too, but generally speaking, over the course of a week, evaporation rates are going to be consistent. If you are losing a few inches of water per week, you need to know how much of that is evaporation and how much is potentially escaping through a leak.
Note, we are not leak-detection experts. If you follow the instructions here and determine that you do have a leak, hire a qualified leak-detection professional to find the leak and fix it.
Evaporation rate vs. Loss rate
The simplest way to identify if you have a leak is to do the bucket test. The bucket test involves drawing a line (or using a piece of tape) to mark the water levels inside the bucket and outside the bucket. Leave the bucket on the top step or sun shelf of the pool for a week and do not touch it. After a week, if the pool's water level has dropped significantly more than the inside of the bucket, it's most likely a leak, though splash-out can also contribute.
The evaporation rate will be inside the bucket, and the loss rate of the pool will be on the outside.
If you are losing more water outside the bucket, hire a professional leak detection company to find the leak and repair it.
Chemistry symptoms of a leaking pool
Another way to tell if your pool might be leaking is if certain parameters are reducing rapidly. These would be factors like Total Dissolved Solids (TDS), salinity, calcium hardness and cyanuric acid.
Evaporation leaves these things behind because evaporation is just pure water. Evaporation leads to the accumulation of these factors, but a leak will reduce them. A leak is the loss of whole water.