I dug up Northfield’s water report and spent some quality time with John Palmer’s “How to brew“. The book can get incredibly technical at times, but still manages to give good general advice, including what to do about water conditions like ours.
I learned that while the specifics of water hardness and alkalinity are very important considerations for all-grain brewing, extract brewers usually don’t need to worry. However, we have incredibly hard water here. So much that this is even a problem for extract brewing, as our incredibly alkaline water can extract hop polyphenols from the cones, producing harsh astringent bitterness. You can avoid this problem by diluting the tap water with distilled or reverse osmosis water at at least a 1:1 ratio.
It’s not all bad, though. Northfield’s water has a profile that is very similar to Dublin, Ireland’s, being very high in bicarbonates, a moderate/low amount of calcium, and low in sodium, chloride, and sulfate. This means we’re in a great position to produce excellent stouts and other dark beers. Mmm… I’m getting thirsty. The highly roasted dark malts add an acidity that helps balance the pH.
From what I read, if you want to brew a lighter beer, and are going all-grain, you’ll probably want to consider dilution or other methods of reducing the bicarbonates, such as boiling or lime treatment. Those approaches come with their own set of concerns, since you may be reducing other vital nutrients as well, such as calcium and magnesium. You can add nutrients back into the water, but figuring out the right amounts can be tricky. There is software that can help you do this. Check out Gabe’s comments below for pointers on that.