First Need XL
I do a lot of camping in the Leadhills area of Scotland, and arsenic and heavy metals have been found there, admittedly in the past, due to the gold mining that went on. I remember going there with my school an awfully long time ago, and being told about the methods used in gold mining back in the industrial age. Hence my use of the above purifier, as the activated charcoal will take a lot of the above nasties out. Not cheap, and worst case scenario is it only filters 125 gallons before shutting itself down and requesting cartridge replacement, but I have absolute faith in it.
http://www.outdoorgearlab.com/Backpacking-Water-Filter-Reviews/First-Need-XL
Good luck finding what you need.