I never had filters or anything in all the years of walking in the Lakes until a few years ago. I got a steripen and the first trip I used it I had 6 days of the shits despite using it properly in accordance with the instructions. I took it on the next trip and it didn't work so I drank from the streams like I used to. I later bought aqua mira and didn't like the taste so got a drink safe inline filter. I know that where i take water from I won't get ill due to experience of taking from those streams however I have it so if away for a few days I'll use it "just in case".
BTW Trail magazine did a test on a few popular Lakes wildcamp spots and if you read the list or nasties you'd be filtering, boiling and using chlorine all at once. It was the same issue doing a review on the popular filters around at the time so I suppose it made for good advertising revenues to do the review and scare readers nearly to death. Or that could be cynical side coming out again. Anyway IIRC it was sprinking tarn and other places in that area near Scafell Pike. I suspect the samples were taken from places you'd not take from such as the outflow of tarns. It is always recommended to take from the inlet to tarns not the outlet and the rule about free flowing for some distance. Always check for nasties higher up such as dead sheep or animals or toilet paper or sanitary towels or nappies. Seriously I have kipped at Angletarn near Patterdale a few times and all the streams around it had toilet paper close to the stream where campers have dipped into thee stream just off the path for a pee. It is popular with outward bounds and coast to coasters so no wonder the area is one big toilet.
I remember as a kid with the cubs filling our water bottles from a stream near the top of loughrigg that ran across the footpath. In fact we took it directly from where the footpath was and none of us got ill. I think magazines in particular can scare people with the water purification thing. The reality is the UK in higher level streams you are less likely to get ill than other water sources. I actually once got ill from nice safe drinking water that was in a new area I was in once. It is possible to get ill just from different water in a different area to what you are used to.
I don't know Dartmoor at all so have no idea how safe it is there but in the Lakes you are generally safe.
BTW I used a traavel tap of my mate a year before getting an inline filter from the same company. The inline is so much easier to use than the travel tap. The tap is all about squeezing the water out the inline is a simple suck or evenforce it through into another container. No comparison in the ease of use with the inline.
BTW I often use the filter with a bladder then the weekend after a atrip use the bladder without the filter and without disinfecting the bladder. If there was anything nasty in the water (some of it is left in the bladder in that week) yet with the growth time of the bugs I still haven't got ill. I doubt anything is in it in the first place.