Water hardness is commonly measured in parts per million (ppm) of calcium carbonate (CaCO3), grains per gallon (gpg), or degrees of hardness (°dH). 

Here’s a general guide for classifying water hardness:

Soft: 0~60 ppm
Moderately hard: 60~120 ppm
Hard: 120~180 ppm
Very hard: ≥181 ppm

For households, hard water can result in unsightly deposits on faucets and dishes, poor soap lathering, and skin irritation. For industries, such as boiler rooms, manufacturing plants, and water softener systems, hard water can lead to significant scaling, which decreases heat transfer efficiency, raises energy costs, and damages critical machinery.