The most basic of water filters is the clean earth filter. Although not ideal for producing crystal clear clean drinking water, it does have the added advantage of filtering out some components that other filters are unable to remove. For instance, a basic clean earth filter can filter out 99% of radioactivity in water making it the go-to filter for nuclear emergencies.
The materials requirement list is simple: Plastic container, water container, gravel and/or pebbles, fine soil. Additional materials (not required): porous cloth.
How to make a clean earth water filter
To begin, punch a small hole in the bottom of a plastic container. Multiple holes can be punched to increase water flow but can reduce the filtering action.
Cover the bottom of the container with about 2-4 inches of coarse gravel. Small pebbles can also be used but are not as effective.
Over the gravel base, add about 4-8 inches of finer dirt.
To filter contaminated water, hold a glass under the hole in the bottom of the container, pour water into the container while catching the filtered water underneath.
Filtered water can be poured back through multiple times to enhance the filtering effect. Regardless, a single pass through the filter removes about 99% of any radioactive particles in the water source.
If multiple grades of soil are available, layer them in the container starting with the coarsest soil on the bottom working your way to the finer soil at the top. Place a porous cloth in between each layer to enhance the filtering effect and produce a clearer grade of water.