Cole McBride has been tweeting a bit lately about water's composition and its affect on extraction. He was suggesting that soft water, in the sub-50ppm range is more ideal for light roasted coffees and that you need at least 120ppm to properly extract espresso. SCAA standard for espresso competition is 150ppm, for reference.

Anyone have thoughts or experience in dealing with water composition and how to adjust it to extract coffee to its greatest potential?