What a fun science experiment for kids! Here we are doing the Rainbow Walking Water kids science project. It is fun and easy. The empty cups fill up and mix colors to form all the colors of the rainbow. This happens because of Capillary Action! Only a few ingredients needed to get started. As a side note: we found the Up and Up brand paper towels work the best. You should see results within a few minutes. If not, try a different type of paper towel.