Portland

Portland's water comes from the Bull Run watershed, a protected forest on the western slopes of Mount Hood where no human activity is permitted. No logging, no agriculture, no recreation. The water collects as rain and snowmelt, filters through volcanic soil, and arrives at the city with almost nothing in it: calcium around 2 ppm, magnesium barely 1 ppm, total hardness of 3–8 ppm. It is some of the softest municipal water in any major American city. For coffee, this near-blankness is both a gift and a constraint. Very soft water extracts aggressively: without calcium and magnesium to bind with extraction compounds and moderate the process, you get high extraction yields quickly. In the right hands, with good coffee roasted for this water, the result is bright, clean, highly transparent cups where origin character comes through with startling clarity. This is part of why Portland became a centre of third-wave specialty coffee.

Stumptown, Coava, Heart, and others built their roasting and brewing around this water. The sodium at 12 ppm is higher than you would expect from such soft water. It is not natural: the Portland Water Bureau adds soda ash (sodium carbonate) to raise the pH and alkalinity, preventing the otherwise corrosive water from leaching lead and copper from pipes. Without treatment, the alkalinity would be closer to 5 mg/L. This means the treated water has a slightly elevated bicarbonate (around 39 ppm) and pH (8.0–9.0) relative to its hardness, which is unusual.

For coffee, the practical effect is minimal: the alkalinity is still very low in absolute terms. If your water is hard and you are trying to match Portland, you are essentially trying to get close to distilled water with a small sodium-carbonate buffer. That is the profile. It sounds simple, but the simplicity is what makes it work.