Snap. You just tend to end up knowing which streams look best.
I’ve drunk it for years when I’ve needed to. And apart from making me look to be over 60 (I’m 24), making my weight balloon, causing most of my hair to fall out and the rest turn nearly white, it’s had no effects on me whatsoever.
Andy, wasn’t that all those bacon butties and irn bru?
Ah, the Derbyshire decomposed sheep water… well I can’t remember, it was a long time ago. I probably had way too many pints of beer that day anyway, so any toxicity would have been well diluted. 
I use a Sawyer filter to good effect to lighten the load when I know there will be water on-route.
Friend Nigel takes a tin cup and that’s it, I don’t mind spending £35 on an insurance policy however. You’d have to be unlucky with running water in the Lake District. I was warned off fell-top tarns due to Cryptosporidium when using purification tablets. I haven’t yet had to dip into one with the water-filter, it’s always been flowing water, but I believe they will take out the parasites if required.
Bravo Colin,
Looks like you had great weather for exploring one of the best areas of the Lake District. For me, it doesn’t get much better than a QRP cw radio, a tent and a night under the stars. The little section from Scoat Fell to Steeple is great. However, I recall it feeling little a bit of a slog back to the car park from there.
I have drunk untreated water from the fells for over 20 years now. I have only once had any problems I can possibly attribute to a stream and that was in this area on a SOTA activation last year. When I did Pillar, I linked it up with a few other hills and tackled it directly from Ennerdale. I filled up my bottle here. There were sheep in the area, but I didn’t see any dead sheep upstream from where I filled up. I had a 24 hour stomach problem after that. This one off incident (in the Lake District) hasn’t made me change my habits. I continue to look for water high up in the fells in a fast flowing section of water. Preferably not on the outlet of a popular tarn.
I had the misfortune of Giardia in South America and that lasted about 3 weeks. A good water filter is probably a safe insurance policy.