Understanding Water Hardness GPG Ratings & Scale Damage to Home Appliances

What is GPG (Grains Per Gallon)?

Water hardness is officially measured in **Grains Per Gallon (GPG)** or milligrams per liter (mg/L). One GPG equals 17.1 mg/L of dissolved calcium carbonate. Water hardness is categorized as follows:
- **Slightly Hard**: 1.0 - 3.5 GPG
- **Moderately Hard**: 3.5 - 7.0 GPG
- **Hard**: 7.0 - 10.5 GPG
- **Very Hard**: 10.5 - 14.0 GPG
- **Extremely Hard**: 14.0+ GPG (San Antonio, Midland, El Paso)

The Hidden Cost of Hard Water Scale

When hard water is heated inside a tankless or traditional water heater, dissolved calcium precipitates out as rock-hard limescale. Studies by the Water Quality Association (WQA) show that a 1/8-inch layer of scale inside a water heater increases energy consumption by **24%** and reduces equipment lifespan from 12 years down to 6 years.

How to Test Your Home's Water Hardness

You can check your city's official hardness benchmark on our city reports or order an EPA-certified mail-in laboratory test kit to verify exact GPG levels at your specific tap.