Let’s check in with some earlier hypotheses about water hardness.
- hardness is a specific measure of minerality (TDS) for limited, “industrial” purposes
I still wholeheartedly agree. I might rephrase and say “hardness is a measure of a specific subset of minerality…” etc. But I realized something else about the use of “hardness” to describe water taste. Here’s a definition from the Water Quality Association:
“Hard water is water that contains an appreciable quantity of dissolved minerals (like calcium and magnesium).
Soft water is treated water in which the only ion is sodium.”
This is one of many muddled definitions I’ve seen where hardness is erroneously used to describe minerality. Let’s reiterate: hardness is a measure of multivalent cations, like calcium and magnesium. There are many minerals that can be dissolved in water that don’t make water hard, like sodium. There’s no such thing as “soft water”; there’s only water that’s been made less hard, or “softened,” by substituting something like sodium for magnesium or calcium. And the WQA is a trade association that represents companies that sell things like “water softeners.” Water softeners will cut down on scale in your pipes and appliances, but they won’t necessarily make your tea water taste better.
- pH–as something like a measure of “net ionic charge”–is the best descriptor of “mineral profile.”
Not correct as such. The concept I was grasping after was ionic strength, not ionic charge. Roughly speaking, ionic strength is the total of positive and negative ions in a solution, and ionic charge is the difference between the positive and negative ions. If something has a net ionic charge, it’s unstable and is looking to balance that charge. Mineral water has been sitting in the ground and has had every opportunity to achieve ion balance. Ionic strength is the squared sum of the valence and concentration of all ions in a solution. If water has a lot of mineral compounds in it, it tends to have a high ionic strength.
So when different mineral molecules are dissolved in water, they recombine with the water’s hydrogen and oxygen. Doing so, these minerals change the availability of the hydrogen, which is to say they change the pH. But different minerals recombine in water in many different ways. Ionic strength is no predictor of pH.
- pH as “mineral profile” combined with TDS as “amount of minerality” may provide a complete description of a water’s taste.
I’m abandoning this position as too reductive. (Others would have done so long ago, but for me it’s an accomplishment.) It may be the case that dissolved minerals affect pH and taste in a correlative fashion. I don’t need to know that right now. I’m satisfied to be a stickler about hardness’s inappropriateness as a descriptor of taste. Maybe I will know more after I come back from THIS!