I was a little tongue in cheek as most of these systems
are for home use and are made of concrete. But they are
cheap.

True 95 to 99% effective for anyone one type of pathogen isn't
that effective compared to other types of filters, however the biosand
removes many more kinds of pollution, as well as bacteria,
virus', and parasites that a pump type filter, charcoal,
or chemical type water purifier cannot match. And they don't
need replacement parts. Your basic backpacking filter
isn't going to do much with arsenic or petroleum.


Usually the biosand filters are used in conjuction with
simple sunlight purification as a second step treatment
(SODIS) for drinking water. This then equals or betters the commercial
methods of individual water treatment.