Chickens seem to prefer going after whatever is "new" in their environment. I like to feed my birds black oil sunflower seeds in winter because the seeds are high in fat and help keep the birds' caloric intake up. But my birds wont touch the seeds if I fill a feeder with them. However, if I scatter a few scoops of the seeds across their run the birds go after the seeds with gusto and then seem to want more. So the spilled water is something new and therefore attractive to your birds.