Learners build a filter from old soda bottles and dirt. They create polluted water, and pour it through their filter to clean it. Leaners discover earth materials such as sand and dirt can be used to trap runoff pollution and that there are limits to what dirt can filter. These observations lead to valuable discussions about pollution. Extensions provided on pages 8 and 9 include building a better filter, a filter for acid rain, and formulating a way to measure filtration rates. Part of the 21-activity guide published by OMSI, No Hassle Messy Science with a Wow. All activities in this guide use household materials and all lesson plans include preparation directions, demonstrations, procedure sheets, cross-curricular connections, and scientific explanation of content.