The aquifer supplying our water here in the desert is quite hard, and deposit of scaly white alkali despoils our evaporative cooler pads right-quick. So, a guy at a home show pushing water softening came to our house. Water tested at 38 grains hardness, 1700 ppm (parts per million) dissolved solids. Those numbers meant an insufficient amount of understanding, to me, so I investigated further.
Hardness is universally called-out in grains per gallon of the water. 7000 grains = 1 lb. A gallon of water weighs 8.3 lbs., so a gallon of water also weighs 8.3 X 7000 = 58,100 grains per gallon. So hardness 38 gr./ gal. means our water is about 0.06 % dissolved hardness materials which are Calcium and Magnesium compounds. No others are considered in the hardness idea.
Now, figuring in all the other dissolved stuff, including the 38 grains, 1700 ppm is about 0.2%, so .06 divided by 0.2 = 0.3 or, about 1/3. Thus, 2/3 of the total stuff in our water, are compounds other than "hardness", likely some nitrates, other salts, hopefully not Arsenic, Cadmium, etc.! imp