We put in a concrete cistern when we moved into our house 11 years ago. It's been a great help for our vegetables and perennials since we're on a well. Any rain we get is channeled from the gutters on half our house into the cistern. We just had two inches of rain. That amount fills the cistern, but when we went to use it, only a few inches was in the bottom. I can't figure out what's happening. And how can we determine what the problem is?