Go back over to the home if you haven't bought it yet. Take a 5 gal bucket with you fill it with water and set it on one of the steps into the pool. Make sure the water levels in bucket and pool are the same. Mark level with a sharpe marker. Turn off the automatic water filler if it has one. Leave for a day or two and come back and check the levels. If the pool is lower than bucket level you have a potential leak. If the pumps are circulating if should give you a pretty good idea if you have a leak and the water is going some where. If the yard is mostly grass and the sprinklers haven't been turned and you have a garden moisture tester you could also take readings around the yard to see if there is a potential leak you cannot see. Most garden stores have testers. You any also want to test the sprinkler system to see if it has sprinklers heads that leak water also.