Water filters are typically made with plastic bottles or containers, sometimes with tree bark. A water filtration project may also call for activated charcoal, napkins or paper towels, salt, coarse and fine sand, and cotton and/or pebbles. Non-poisonous grass can be used for a mesh. Muddy or dirty water, once filtered and running clear, is not necessarily bacteria free.
Sand particle size may affect the effectiveness of a sand water filter. Grains should not be too soft or fine, nor should they be too large. Grains of sand used in a water filtration system should range from small to medium sized, and the larger particles should be separated from the smaller particles. A science project for kids to experiment with different types of sand is to run "dirtied" water through them to see which sediment size makes the clearest water. Dirtied water can be made up by adding mud, cooking oil, or some other non-toxic contaminant.
You can use soil and plants to show kids how dissolved minerals move through soil. Some types of materials or nutrients that are food for plants can become pollution if they get into a water plant filtration pump, called an aquifer; where water is processed for use and drinking. Plants do not absorb all ground materials and not all water pollutants are nutritional for plants. A science fair project can be used to show how plants filter water by using potted household plants, clear containers, powdered drink mix, vegetable oil, and a couple of household cleaners.
Clean water is a must for survival. Water that is free of impurities and pollution is called potable water. Filtered water is not bacteria-free and is still capable of making a person ill, sometimes even fatally. A good science project for kids is for them to show how special chemical treatment and/or boiling still needs to happen in order to purify the water. Kids can make a mini water plant to show how the separate processes of aeration, coagulation, sedimentation, filtration and disinfection are used to purify water after it is filtered.