Water Torture Part 2

So thanks to coffee ingénue Ben Kaminsky, I got my water measured.

To recap: a couple weeks ago, our water was reading at about 40-50 TDS (total impurities), the ‘book’ says about 150 ppm TDS is ideal for brewing coffee, and my water is now reading about 140-150 ppm TDS.

Ben measured my water to be at 8 grains of hardness.
hardness = Calcium Carbonate (CaCO3) content
1 grain = 17.1 mg/L (mg/L and ppm are about the same)
8 grains of hardness = 137 mg/L CaCO3
“the book” says 3-4 grains (51-68 mg/L) of hardness are ideal for brewing coffee.

So my CaCO3 content is really high. CaCO3 is an acid buffer, and sure enough, the coffee tastes like you magically removed most of the pleasing acidity. I guess I’ll use bottled water again until the utility goes back to producing harder water. Apparently our water utility has changed where the water is being sourced (this sort of thing is very common for high-population areas).

At this point, I have more questions than before:
Why does “The Book” say 3-4 grains is ideal? Why not lower, or _no_ CaCO3?
Why is it 150 ppm TDS ideal? How much of this is a valid rule-of-thumb, and how much of this is a lowest-common-denominator?

I’m finishing typing this up as I’m waiting for a couple cups of coffee to cool. As an experiment, I brewed them with distilled water. I’ve also reached out to some of my water-expert colleagues out there. Stay tuned, more to come.

<— photo of what happens when you have even 6 grains of hardness

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