Peppersass wrote:According the Jim's water FAQ, the alkalinity level is one of the determining factors in scale formation. So, 40 ppm might not be quite as safe as it might appear.
Scaling is determined but the Langelier index, an equation that has hardness, alkalinity and pH as variables. You can replace actual pH by equilibrium pH, and replace equilibrium pH by a function of alkalinity. Once all the math is massaged, the effect of alkalinity on scale formation adds up to roughly double that of calcium hardness. However, the scaling potential is multiplicative, not additive, so removing either calcium hardness or alkalinity removes all the scaling. This is why cation softening works, despite leaving alkalinity unchanged.
In terms of corrosion prevention, alkalinity dominates, so cation softening is much safer for equipment than anion softening or complete demineralization, since very hard water, cation softened, will neither scale nor corrode. However, very hard, cation softened water makes for slightly dulled coffee. Given the fashion for overly bright espresso roasts, this may actually be a good thing. But it is unacceptable for high end regular brewing, and a compromise for properly balanced espresso blends.
In natural water, alkalinity is almost always less than calcium hardness, typically 66%. Mostly, you can take the TDS of the water and figure it's 60% calcium hardness and 40% alkalinity. If your titration measurements are far off this, you probably made a mistake, since if the water minerals are mostly magnesium and calcium carbonate, that is the proportions you will see by chemistry. The usual reason for mistakes is stupid unit tricks: TDS meters and ppm measures are in CaCO3 equivalents; if you use molarity or molecular weight, the German or chemist's unit of measure, the proportions are very different (alkalinity shows up much higher).
I suspect this discussion and some of the fear of scale may be shadowed by stupid unit tricks. The Chicago water I use is 150 ppm, 90 calcium and 60 alkalinity, measured in CaCO3 equivalence units. This is neutral water and optimal for coffee brewing (arguments about magnesium versus calcium aside). For me, it requires a flush descale of the steam boiler every two years or so with one cappa and three or four shot a day on average. A tear down descale would be required every ten years. There are some very hard water areas in the US, LA being the standout in terms of population. But a reverse osmosis water treatment with mixing that got to 150 ppm would achieve the same results in these areas; and be the simplest way to produce high quality water. The new cartridges with dual catalyst beds would work just as well, but it seems we still need a simple and fool proof way of adjusting them.