I work in the Biology labs for United Utilities (for my sins!) and one of the main tests we do is looking for Crypto, and occasionally Gardia, in treated and raw waters (riveting, I know
) Periodically there is a practitioners meeting where we meet with the likes of Scotish water to discuss results, practices etc.
Crypto and Gardia are a hell of a lot more prevelant up in the highlands than they are round our patch. A typical litre of lowland raw water could contain tens of either of these oocysts, but bear in mind this is water reaching treatment plants so the samples are taken right from the bottom of the valley.
Despite this I am quite happy to drink untreated water when I am up in the hill, you just have to be sensible about where you take it from. I always try to take water above the 800m contour, never from below human habitation and always take it from the fastest flowing part of the stream. Always boiling standing water goes without saying, and taking extra care around the lambing season as mentioned above is worth thinking about. I always carry chlorine tablets as well, just in case
