This device will automatically add water to your pool when it gets below a specified level. It does this all for under $15. By having a device fill the pool to a specific level, you can avoid wasting water by overfilling.
Step 1: UPDATE: VERSION 2.1 Cross Section Added For Stability
After version 1.0 kept falling over in the water, I added a cross section for stability. I spray painted the PVC Black to help protect it from the sun. It also makes it look much more finished.