In Canada, CAWG developed a rainwater storage tank with biosand layers that can purify rainwater for drinking, which could be especially helpful for residents in Caribbean islands where water supply interruptions are common during hurricane season. Biosand filters remove up to 96.5 percent of bacteria and up to 99 percent of viruses from rainwater.
The biosand filter is filled with layers of specially selected and prepared sand and gravel which removes pathogens and suspended solids from contaminated drinking water. A biological community of bacteria and other micro-organisms grows in the top 2 cm of sand, called the biolayer. The micro-organisms in the biolayer eat many of the pathogens in the water, improving the water treatment. The tanks can range from 200 gallons for household use to 600,000 gallons for larger, industrial type use.