Hey guys just weighing in here... IMHO there is no reason to think that raw (or hard) water would be, in any ratio, a good thing for brewing. I have done several testings with raw vs. R/O water as I used to be a distributor for water purification systems... the tap water by itself may taste fine but it's the reaction with the hardness and dissolved solids in the tap water with any dissolvable substance (like grains/malt extracts) which can greatly effect the desired flavor... why have anything but the truest flavor of your barley beverage which treated water can provide... A simple and great visual test that I have demonstrated many times for buyers (when I was a distributor) was this: Simply make some orange pekoe tea .. One cup with tap water and one with R/O or distilled water... Notice not only the obvious visual difference but the flavor as well. This is a great demonstration to keep in mind when considering your brewing because it is the same concept. Again this is one mans voice and to each his own... Just my 2 cents! Cheers