A water filter science experiment makes a fun and educational rainy-day activity for kids. This filter, made mostly from inexpensive household items, will teach kids about the processes water purification plants use. Putting the filter together is a simple process, easily done on a tabletop in an hour or less.

Cut the soda bottle in half, and remove the top half. Put three layers of cheese cloth over the narrow mouth of the bottle and use rubber bands to hold them in place.

Put the top half upside down into the bottom half so the top half makes a funnel, and the bottom becomes a collector.

Add layers of sand, gravel and charcoal into the top half of the bottle. If you’re working with several groups of children, have them try the layers in a different order and see which arrangement works best. For example, one group adds sand, then activated carbon, then gravel. The sand is at the bottom, and the gravel is on top.

Get some dirty water. If you do not have dirty water you can make some water dirty by using cooking oil, dirt, bits of food, etc.

Pour dirty water into the top half of the bottle. It should run through the sand and gravel, out the cheese cloth and come out clearer in the bottom half of the bottle.