JWR,
I found the recent water filter article interesting and appreciate all the time Scott spent researching water filters. I set up filters for missionaries in Third World countries and have found that plastic water containers can promote bacteria growth. I believe there are two causes: 1. The plastic scratches when cleaning and provides a place for the nasties to attach and hide on the sides of the container, and 2. The container allows sunlight to enter which also encourages some types of bacteria.
Another problem with only using mechanical filtration is some viruses are physically impossible to filter out of water (i.e. rotavirus). For this reason we add a final stage of purification, UV light (battery powered). Once all the particles are filtered out, UV light is extremely effective in killing anything that’s left. As far as I understand it, carbon filters remove viruses as well, but the problem is you never really know when the carbon is “full” and can’t absorb any more material.
That said, I’m pretty sure I can’t identify the missionaries who use plastic drip filters by their bad health. – Kevin K.
Letter Re: The Water Filter Quest
