Instead of buying expensive commercial filters and stockpiling them, another option is to build a bio-filter. This simple filtering system is used worldwide to purify water for drinking. While it may not get out every pathogen in the water, it will get out enough that you can safely drink the water, allowing your body to destroy the few that manage to get through the filter.
Bio-filters have three separate layers:
3. Activated charcoal
The first layer, gravel, is there to remove large pieces of debris from the water. This would include things like small sticks, leaves, the odd tadpole and bugs. The water then moves on to the sand layer, which removes smaller particulate matter that managed to pass through the gravel. Finally, the water passes through a layer of activated charcoal to remove bacteria and some chemicals.
To assemble your fittings and build your filter, do the following:
The fitting that is going to go on the inside of the bucket needs to have fiberglass screen stretched over it. That can be held in place with a rubber band or O-ring. However, gluing it makes it more secure. Cut a hole in the bottom center of two buckets, which is the right diameter for the threaded part of the fitting to go through. Cut the same size hole in the side of the third bucket, which is just above the bottom.
Attach the fittings together, with the bottom or side of the bucket between them. The screened side of the fittings should be up. Use an O-ring between the fittings to create a seal.
For the bottom bucket, the one that has the fitting through the side, you may want to add a valve, an angled fitting or a fitting with a flexible tube for the outlet. Whichever you choose should allow you to have the filtered water go into a fourth bucket, pitcher or other container.
Cut a hole in the center of the lids for two of the buckets, which is slightly larger than the fitting. You don’t need a tight fit here, rather one that will make it easy to stack your buckets.
To protect the screen from the weight of the sand and gravel, put a cover over it. The easiest way to make this cover is with some small plastic cups. Drill a number of holes in the sides of the cups, so that the water can get through. Then glue the cup upside-down over the fitting.
Before putting your gravel, sand and activated charcoal in the filter, it needs to be rinsed thoroughly to remove all dirt and silt. When you can put on these materials, without any dust fogging the water, then it is rinsed thoroughly enough.
You will need to fill each bucket 2/3 to 3/4 full of the filter materials. The activated charcoal goes in the bottom bucket, which should be the one with the fitting on the side. Put one of the lids with the hole in it on this bucket. Set the bucket for the sand on top of it, and the bucket for the gravel on top. The top bucket’s lid does not need any hole in it. A plain lid can be used to keep any debris from falling into this bucket.