Nature's Mineral Water?

When you put a small mineral block on the ground in the woods, deer will lick it until the rains eventually dissolve it. Once the block is gone, the deer will eat the clay containing the minerals, and after a couple of years you have a pretty good size hole in the ground.

Then, when heavy rains come, the clay base of the hole holds water for a few days. The deer seem to enjoy the resulting salty mineral water - while ignoring the apples I left them.