While experimenting with the SODIS (Solar Disinfection) method of water treatment, I went off on one of my frequent tangents and tried a couple of ways to filter water before disinfecting it in the sun. For SODIS to work, the water has to be clear enough; if it’s too turbid, the UV rays can’t penetrate the water deep enough to kill the germs.
So what do you do if the water is too cloudy? Make a simple cloth and charcoal filter. You could also use some packed, dried grass, or even sand. Another advantage to filtering the water before SODIS is that SODIS is NOT water purification. Even though the pathogens are killed by the UV rays of the sun, the water still contains mud, frog poop, and other things that make it taste like pond water. Filtering it, especially if you use carbon, will remove much of this junk and vastly improve the taste.
How to Make a Bushcraft Water Filter
In this example I use bamboo, but you could use a plastic water bottle with the bottom cut off.
I tried two methods. First, I packed some charcoal in a shirt sleeve and stuffed it all into the bamboo section. While I’ve used this method before, it’s very slow because there’s so much tightly packed fabric inside.
Second, I placed a cloth plug in the bottom, then poured some crushed charcoal, then covered that with another cloth plug to keep the charcoal from floating. Thanks to Nick, the cam op, for this idea.
The second method works much better. The water flows quickly, and while I didn’t show this in the video, I did taste it, and it tastes much better than the unfiltered pond water. However, it still needs to be disinfected after filtering, so I don’t recommend drinking it straight out of the filter; most commercial filters have pores small enough to filter out bacteria and other pathogens, but this backyard contraption doesn’t.
- Cut out the longest, widest bamboo section you can find. Leave the joint in one end.
- Cut a pea-sized hole in the bottom.
- Stuff a piece of cloth into the bottom. You don’t need it tight; you just want it to cover the hole so the charcoal doesn’t wash out.
- Pour 3 or 4 inches of filter media. In this case I used crushed charcoal (make your own charcoal).
- Cover with another plug of cloth.
- Fill with water.
- The first bit of filtrate will have a lot of charcoal powder. Discard this; it is too dark to use for SODIS water treatment.
Results After Filtration and Solar Disinfection
This is an effective way to clarify water for SODIS, and it improves the taste. As I mentioned previously, the charcoal greatly improves the taste, and I’m sure removing mud and frog poo plays a part as well. The water did taste a bit woody; this is either from the bamboo or from some incompletely carbonized hardwoods, but either way, it is much better than the original, unfiltered pond water. The filter should get better the more you use it.