The minerals historically used are calcium chloride, magnesium sulfate, magnesium chloride, sodium bicarbonate and potassium bicarbonate; calcium carbonate, calcium sulfate and calcium citrate exist but are harder to find or to dissolve, the citrate acting on alkalinity through an anion different from bicarbonate. Food-grade minerals are required: laboratory grades, which are purer, may contain impurities unfit for consumption, heavy metals included.

And the hydrated form must be read on the label: a hydrate carries a fixed number of water molecules that weigh on the scale. Weighing calcium chloride believing it to be anhydrous when it is tetrahydrate seriously underestimates the calcium added. Calcium chloride is sold mostly anhydrous, as small white spheres; magnesium sulfate mostly heptahydrate, which is Epsom salt, transparent crystals like snow; magnesium chloride mostly hexahydrate, large milky flakes; the bicarbonates have no hydrate.

Three properties to set, alkalinity, hardness, magnesium-to-calcium ratio, and five ingredients: there are several combinations for the same water. The choice between magnesium sulfate and magnesium chloride is historical, it is not known whether the anion changes the taste; the choice between sodium and potassium bicarbonate may matter a little, since sodium can mark the profile slightly, far less than magnesium and calcium.

Gagné 2021, pp. 26-29 Gagné 2021, pp. 26-28