Simple And Free Bio Sand Water Filter From A 2-Liter Bottle
Want a way to filter water to near tap-quality for free?
Without spending a dime, you can construct a very effective bio-sand water filter from a recycled 2-liter bottle that, if built well, can remove almost all contaminants, including water-borne pathogens. Followed up by solar water disinfection (SODIS), you can easily produce safe drinking water with no cost whatsoever.
The main reason you probably haven't heard of a bio-sand filter is that it's a fairly recent discovery that came out of efforts to provide clean drinking water to developing countries.
In the video below you'll see a student demonstration of simple biosand filter constructed from free recycled items -- a 2-liter PET bottle (food safe), ordinary sand (pre-washed), and a bendy drinking straw. I'm sure you'll be impressed by how well it filters the muddy water into crystal clean drinking water. Of course that's just the surface appearance, but research has shown that if it's constructed properly and used correctly, even a simple "demo" model like this can remove up to 90% of contaminants, enough to complete the process with Solar Disinfection (SODIS), just by leaving a bottle of clarified filtered water under the sun's ultraviolet rays.
But despite it's effectiveness, there are also a few reasons why most First World consumers won't be replacing the Brita filter on their counter with one! The reason it's so much more effective than an ordinary sand filter -- the kind used not only in swimming pools, but in the early stages of your municipal water filtration system -- is that it utilizes a naturally-occurring layer of sludge that accumulates on top. That important sludge layer is actually a community of friendly bacteria that literally EAT a large portion of incoming water-borne pathogens.
Since the functionality of the biosand filter depends on the health of that microbial culture, you need to give it time to grow, and make special care both keep it wet, and not destroy it with chemicals, which... let's face it, are in pretty much everything in your house!
Where biosand water filters are best used is in an off-grid situation where you're collecting rain or river water, or possibly attempting to recycle reasonably clean greywater, on a consistent basis.
Because the bacteria culture grows to mirror the microbes in the water source, the consistency of source water is important. This also makes a biosand filter not-so-ideal for an emergency survival situation, unless of course you're stuck in one place for awhile.