In this activity on page 7 of the PDF (Water in Our World), learners make their own water treatment systems for cleaning water. Learners construct two filters to test: one with sand and one with sand and charcoal. Learners compare how well the sand and sand + charcoal filters clean water that is "dirtied" with food coloring, dirt, and grass. This activity also features a list of ten ways you can conserve water. Safety notes: Adult supervision is needed for this activity. Do not drink any of the water samples in this activity. Make sure to follow the safety tips listed on page 3 of the PDF, as well as those listed in the procedure for the activity.