HI

It might not be as big an issue as you think

Over the winter, water on the cover and an ice plug in the pool can push out the amount of water you tend to loose.

A wet spot tends to indicate a leak. If you search the Forum, you'll find posts on how to use dye to 'pinpoint' the leak. If you want to use the water level to narrow down the level of the leak - you need to let the pool leak until it stops loosing water and then inspect around the water line. (this can be VERY bad for the liner, if the leak is deep!!)

Al (Poconos) has posted some very ingenious ways of making test dye and patching a hole on the bottom - without getting wet Try searching and see if you find helpful info - if you don't, I'll help link them for you and proffer my advice.