Giardia is widespread in water right across the UK, never mind Europe; fact. I know cos I had it a few years back and it's quite unpleasant. My lovely wife contacted the national water inspectorate (I think) who told us how common it is. Of course, you can drink clean looking water if you wish, and risk this nasty, lingering tummy bug, but I wouldn't. Correction, I would if it was life or death, but that's unlikely in the UK.
Keep safe; use a water purifier like the General Ecology First Need, one of the best on the market and easy to use plus, importantly, field serviceable without tools.