How the math works
Softenry mathGrains per gallon = mg/L (or ppm) as calcium carbonate ÷ 17.1. One German degree is 1.043 grains per gallon. Weekly grains = people × 75 gallons a day × gpg × 7.
BandsBands follow the usual water-treatment scale: under 1 gpg soft, 1 to 3.5 slightly hard, 3.5 to 7 moderately hard, 7 to 10.5 hard, over 10.5 very hard.
Questions
My water report says 200 ppm. How hard is that?
200 ppm as calcium carbonate is about 11.7 grains per gallon, very hard on the usual scale.
Are ppm and mg/L the same?
For hardness in water, yes: one part per million is one milligram per liter.