Many, many years ago, when I was in college, I ran the municipal swimming pool in our fair town for 3 summers. Now, by "ran" I had zero to do with lifeguards, concessions, whatnot. I was the ugly kid who was given the task of making sure the PH levels were fine, that the ratio of piss to water was satisfactory, switch over the chemical tanks when they ran low, visit with the health department when they came out periodically to test the water etc.
The pool held 1.2 million gallons. It would easily lose on average around 20,000 gallons per day from evaporation, people splashing water out, cracks in the bottom of the pool, people getting out of the pool and having water drain off of them, etc. The pool had two 4 inch faucets that were used to fill the pool; we would open up one of them partially to top off the pool after it closed for the day.
My last summer there, they hired a company that came in before hours, put on scuba equipment, and were to "seal" the cracks in the pool with some special caulking that was supposed to cut the water losses in half, but after they were done, we still were losing around 20K per day.