The questions you will answer in this FACTivity are: Which land cover best protects water quality and why? Materials: 3 paint roller pans Shovel 3/4 cup liquid kitchen oil (such as canola oil) 2 gallons of water in plastic jugs One garden sprinkler can Blue or red food coloring Topics: Water, Agriculture, Erosion, Experiment, Graphic Organizer, Human Impacts, Land Cover, Pollution.