EXPERIMENT 7

A MODEL WATER FILTER

THINGS YOU NEED: The juice container from Experiment 3 (or another one like it). Stocking from Experiment 2. A few cups each of pebbles, gravel, coarse sand, and fine sand (you can probably get all these for nothing at a construction company). 2 feet of wood 8 inches wide. Collecting bowl.

Water. How precious a gift. Next to air, it’s the most important thing in our lives. Without water in any form, a person wouldn’t be able to stay alive for much more than a week.

The average American uses about 70 gallons of clean water each day at home. But because of the extent to which water has been polluted, clean water is becoming more difficult to produce. It’s easy for a water treatment plant to remove debris, suspended impurities, and disease germs. But dissolved chemicals and pesticides are something else. Scien tists are attempting to develop ways of preventing such pollutants from getting into the water in the first place.

The model water filter featured in this experiment represents part of a basic purification process used by many cities to treat their water. The process consists of 1) coagulation and settling, 2) filtration, and 3) disinfection. Filtration removes not only solid impurities but some bacteria too.

All right, let’s go to work and build our water filter. Tackling the stand first, saw two 6-inch pieces off the wood. These will be the legs of the stand. The remaining piece will be the top. Cut a 4-inch diameter hole in the center of the top so that it can support the container. Then nail the stand together.