Modern water filtration devices, such as pitcher-style filters and faucet filters, utilise advanced filtering technologies, like activated carbon and ionisation. However, there are several simpler, more primitive water filter technologies available as well, which children can re-create for science projects or just for fun. These simple water filters utilise inexpensive, household items as their primary components.
In its simplest form, a fabric water filter can consist of a glass beaker, a swatch of fabric large enough to cover the top of that beaker and an elastic band to hold the fabric in place. To operate the filter, you use an eyedropper or other type of liquid applicator and apply drops of water on top of the fabric. Because water molecules are small in relation to common water contaminates, like dirt, water will be able to seep through the fabric while the larger contaminates will become stuck. For optimal filtering results, use a tightly woven fabric, like silk. For fast filtering results, use a looser woven fabric, like cheesecloth.
Sand Funnel Filter
A sand funnel filter operates using the same basic filtering technology as a fabric filter. However, instead of relying on woven fabric fibres to catch contaminates, a sand funnel filter utilises grains of sand. Building the filter requires that you cut a circle from a piece of paper towel and fold it into a cone. You then place the paper towel cone inside a funnel and fill the cone with sand. To operate the filter, you simply pour dirty water on top of the sand and place a cup or glass beneath the filter to catch the results.
Building a layered filter requires that you take the sand funnel filter design and incorporate some different filtering media in addition to the sand. For example, you could use a layer of sand at the bottom of the paper towel cone, a layer of gravel on top of the sand and a layer of cotton balls on top of the gravel.
Water Cycle Filter
A water cycle filter purifies water through evaporation and condensation. When liquid water particles evaporate and become gaseous, they leave contaminants, like salt and dirt, behind. When these same water particles condense, returning to liquid form, they are much cleaner, as they no longer carry contaminants. The trick to harnessing the natural water-filtering powers of evaporation and condensation is placing a small container, such as a cup or mug, inside a larger container with a wide opening, such as a plastic or metal bowl. Pour water into the bowl, surrounding the cup, and cover the opening of the bowl with cling film. By exposing the bowl to direct sunlight, you can evaporate the water at the bowl's bottom. The gaseous water particles will rise and -- after making contact with the relatively cool cling film -- condense and fall down into the cup.