Each group needs:

• Data Collection Worksheet, one per student
• 2-liter plastic bottle cut in half horizontally, as shown in Figure 1; ask students to bring empty bottles from home or get from local recycling center near you; wash before use; consider using the same ones used in Lesson 4's This Landfill is a Gas activity.)

• 3-inch square of mesh, such as fine nylon screen or fine cheese-cloth
• 1 rubber band
• 1 spoon or other stirring utensil; a chopstick works well

To share among all groups:

• filter materials, such as filter paper or large coffee filter (at least 6" in diameter), 6 cotton balls, ~6 cups soil, ~6 cups sand, 1 dozen large and small pebbles (total), ~6 cup activated charcoal (such as used for potting plants and in aquariums)
• aquarium aerator or a mechanical stirrer/mixer; aeration pumps for fish tanks work well
• measuring cups
• 2 large jugs/jars, ~1 gallon size, such as plastic gallon milk jugs with lids; for mixing/storing "polluted water" (recipe follows)
• "polluted water" made by mixing the following items in amounts at the teacher's discretion: water (enough to fill the jugs/jars ~¾ full), green liquid food coloring, soil, organic matter such as grass clippings and orange rinds, dishwashing detergent, vinegar, baking soda, salt, pepper, pieces of polystyrene foam (foam peanuts), small pieces of newspaper, and your own ideas for other items