I've got a full barrel of rain water, and the lawn doesn't need it yet. So you know what I'm thinking. But has anyone tried it? Will the taste of eavestrough be too strong? Or is this idea so crazy it just might work??

My understanding here is that rainwater is similar to distilled water as it is evaporated then condensed. As mentioned though it will probably pick up some environmental comtamination through this process as well as sitting in the collection vessel. Not a big if your all grain brewing as you will be boiling it. This would also mean it is basically void of the key elements CaSO4 (gypsum), NaCl (Table Salt), MgSO4 (Epsom Salt), CaCl (Calcium Chloride), NaHCO3 (baking Soda) and CaCO3 (Chalk) which could be seen as a good thing as you can easily make these additions to your water and customize it to your liking. There is lots of good information out there on the internet to help you set up a target water profile as well as figure out how to reach that target. BeerSmith has a great water profile tool in it and I am sure that other brewing softwares do as well.

I would agree with Duncan on this one. I was just reading New Brewing Lager Beer by Noonan, and he writes the following on the subject:

"All naturally occurring waters are dilute solutions of minerals in which small quantities of gases and organic matter may be dissolved. Rainwater should be the purest natural source of water, but because it assimilates atmospheric gases and organic mineral particles wherever the air is the least bit polluted, most rainwater is absolutely unsuitable for use in brewing. Precipitation in areas far removed from large fossil-fuel burning plants more often than not is still polluted by highly corrosive sulfuric acid. Free hydrogen carbonates...are also common in rainwater. They rob the calcium from the mash, wort, and ferment by forming bicarbonate salts that are precipitated from solution during boiling."

Based on that, I would just avoid the issue altogether by using regular water that you treat to remove the usual suspects - chlorine, chloramine, etc. If you do get adventurous and throw caution to the wind, let us know how it turns out! Good luck!

I also agree with Duncan. I'd avoid that rainwater. My sister just looked at a house for sale that used rainwater as grey water and even without using it as drinking water, there were several filters and UV light treatment for it. Something to do with how long it sits.

I personally just fill up primary's with tap water and let it sit for a few hours so the chlorine dissipates. I guess you could always run to a grocery store and get the 19 L blue jugs of "spring water". I used to do that for expensive wine kits.

I use a carbon filter that I picked up from Can Tire for around $35 or so. I rigged it up with a quick disconnect to hook up to my garden hose, and the water really rocks through it. I find it more entertaining than the tablets - the more cool equipment I have, the better!