I am familiar with filtration vs purified.....we didn't expect it to remove everything. Yes we knew it would remove the 'large' chunks....and I am not so naive as to think it was purified......I did however expect there to be some (even slightly) lower numbers of organisms.....I figured that the sand with the coffee filter would do a bit better than it did....and we did start with the gravel > the sand > coffee filter. There was (what I thought was) a decent amount of sand for the water to filter through. We didn't use that much in the way of gravel as we only expected it to get the large stuff....the water did take a decent amount of time to drip through (read that as slowly) so we expected (if nothing else) a "Slightly" better result......were we suprised.......but I agree that it brings up the question....how many people out there have the idea that a similar set up would be good for them? Is there an easier way to accomplish the same goal with less a bulkly set up?

Oh and no the instructor was the first to say..."This is only FILTERED !!!NOT!!! PURIFIED!!! so DON'T drink it." They were surprised though at our results.....

The class was a discussion of things that 'civilizations' need to survive. Water being so precious, the instructor thought that this hands on project would give them an idea of how much you need to do to get 'cleaner' water....the kids realized how hard it is to find clean water........