Bio-sand water filters are fascinating: A simple combination of cement, sand, gravel, and gravity (with the help of some microorganisms) can eliminate worms, protozoa, bacteria, and viruses, making once unsafe water drinkable. Women can spend less time transporting water from far away, and children can miss less time away from school due to water-borne illnesses.
There are 4 filtration processes involved:
1. Biological Layer— organic matter gets trapped in the first 2 cm of sand and develop a complex food chain that digests pathogens.
2. Mechanical Trapping— other pathogens get trapped in sand as water filters down by gravity.
3. Adsorption — a static charge traps even more harmful stuff.
4. Natural Death — with little food and light, pathogens eventually die off.
Here’s a few simple diagrams about how they work:
from cawst.org
from cawst.org
(from the cawst.org website)
What’s so great about the water filters is that they can be built on site in Cambodia at the Trailblazer Foundation headquarters. Thanks to Heather for the inside glimpse of the filter-making workshop over in Siem Reap!
Heather sifting bio-filter sand. (Photo courtesy of Heather Gaines)
(Photo by Heather Gaines)
(Photo by Heather Gaines)
(Photo courtesy of Heather Gaines)
(Photo by Heather Gaines)
(Photo by Heather Gaines)
After delivered, an installed water filter can last for decades. Furthermore, the sand never needs to be replaced! According to cawst.org the filter has been tested to remove up to 100% of worms, up to 100% of protozoa, up to 98.5% of bacteria, and between 70-99% of viruses.
Heather assures me that she is living proof of the effectiveness of bio-sand water filters. She drank every day from one of the first filters made by Trailblazers, installed at the Siem Reap office.
(Photo by Heather Gaines)
I’m a bio-sand water filter believer! I hope you are too.
To donate to my fundraising project, please go to my FirstGiving page. Donations are tax-deductible. $5 makes a difference, $60 buys a filter.
Marisa Walks Across 