CoyoteOldMan At the very least, to avoid scale, check that total residuals are below 100 mg/l (and even then). Tesco’s Ashbeck is decent for that, and it’s cheap-ish, at 26p/litre (total hardness as CaCO3 42 mg/l). Waitrose’s “essential mineral water” has over twice the Ca and Mg content of Ashbeck (total hardness as CaCO3 90 mg/l) -
Residuals below Xmg/l is fairly meaningless, as is comparing hardness from Calcium and Magnesium.
Scale is a combination of hardness from Calcium and Magnesium* and alkalinity from carbonate sources (bicarbonate in solution). You’ll get scale depending on the balance between hardness and alkalinity, and the saturation, and the temperature. How much potassium or sodium is irrelevant hence the useless nature of dry residue measures and TDS.
CardinalBiggles
To determine scaling potential you need to know the hardness from Mg and Ca as CaCO3, alkalinity as CaCO3, and the temperature. Put these things into my spreadsheet and you’ll see if the water will form scale or not…
I wouldn’t descale the brew boiler before determining if the water will have formed scale at the brew boiler temp. The water may scale at service boiler temps, or it could be that scale only starts to form when you’ve concentrated the minerals over time when steaming milk (water is lost to steam; minerals are left behind - repeat), this can happen quite quickly, say a week of daily steaming, even with something like Ashbeck.
*there are other types of scale e.g sulfate and silica but not really worth mentioning those.
On another note: regardless of how the filtration works on the end of the tube so it gets sucked up by the pump or dumped into the thank, you can use a blind filter and collect water from the return hose from the OPV and do a test with a GH/KH drop kit.
