North America has an extensive problem with Giardia infestation which, in the wild, is apparently spread through the deer etc. I've spent time in the mountains of Vancouver Island, Canada, as well as in the Canadian Rockies and am well familiar with the "beaver fever" problem and that one cannot drink water from, what appears to be, a fresh bubbling mountain stream. It wasn't always like this - I have friends tell me that up until the 80's they never bothered purifying the water in the wilds of Vancouver Island. Apparently it is relatively OK to drink untreated water very high in the alpine, and I did drink directly from a spring once in the Rockies.
The Berg does not appear to such a problem with Giardia - we would all know about it, since I don't think you can build up an immunity to it. I know from my trips to Nepal that once you get Giardia you have to treat it medically. There is undoubtedly some degree of contamination in the Berg, but more in the way of bacteria and foot-and-mouth (seen cases of both in hiking buddies) - theoretically it is possible to contract Giardia there, though I don't think its common. I am picky about where I drink there though (I take care around grazing areas, smuggling routes and popular hiking routes), but it is largely still safe and one of the things I really treasure about the Berg.
We so easily take fresh water for granted! A fresh reminder to conserve, protect and cherish the Berg!