To repair a leak in a pool liner, you must first find it. Use a 5-gallon bucket filled with water to determine if there is a leak. Use food coloring mixed with water in a spray bottle and determine where the pool is leaking.
Evaluate the leak
When the weather is hot, water evaporates from the pool rapidly. Determine if you actually have a leak before spending time trying to locate a nonexistent leak. Fill the bucket with water. Set it in a location where the level of the water in the bucket is about the same as that in the pool. Use a tape measure to determine the inches of evaporation per day in the pool and the bucket. If they are approximately the same, you don't have a leak.
Find the leak
Spray the colored water around the edge of the pool and watch for flowing color. If the food coloring dissipates into the water, move and spray the next spot. If there is a leak, the colored water flows toward and out of it.
Check the bottom of the pool
Leaks in the bottom of the liner often erode away the support sand, leaving a depression. Dive to the bottom of the pool with the spray bottle. Squirt some colored water into the area and watch for a flow toward the leak.