In order to provide Dublin with an adequate potable water supply, the Grand Canal was built. It also serves as the water source for the Guinness brewery which is conveniently located bankside.
I'd assume some level of treatment is performed, whether by the utility or by the brewery itself, but the brewery would only really need to filter out particulates, as the process of making wort requires vast amounts of boiling.
Ah, I see. Was just sceptical of water from such an open canal being used to make a beverage, but if the process as such sterlizes it, then it should be no problem.
Cool Picture though