Read the date and source before the hardness number
Check the reporting period
The table now posted by Norman is labeled 2024 and covers July 2023 through June 2024. Treat those dates as part of the result. [1]
Identify the water source
The page separates treatment-plant water from well water because their average hardness values differ. Do not combine them into one unexplained city average. [1]
Confirm the unit
The city reports total hardness in milligrams per liter as calcium carbonate. A softener control may ask for grains per gallon instead.
Use a property test when settings depend on it
A city value is useful background. Test the feed water when softener sizing or another equipment decision needs the hardness reaching that property now.
Hardness describes minerals, not every water problem
Hardness may help explain
Hardness does not prove
Scale on fixtures, soap behavior, and mineral deposits in heated equipment.
That a leak, odor, corrosion spot, or appliance failure was caused by hard water.
Why a softener setting or maintenance plan needs a measured input.
That every Norman address receives the same water blend on every date.
The mineral-loading question a treatment product is designed to address.
That the product removes germs or a health-related contaminant; product claims must be checked separately. [2]
When a property-specific test is more useful
- A softener or commercial process must be sized from a dependable current value.
- The home has a private well, another utility, or treatment equipment that changes the incoming water.
- The observed scale does not match the utility information or differs greatly between fixtures.
- A health-related concern is being investigated. Hardness data is not a substitute for testing the substance of concern. [2]
Convert mg/L to grains per gallon
Copy the value with its label
Write down the mg/L value, source, and reporting period. A number without that context is easy to misuse.
Divide by 17.1
Norman gives the conversion: mg/L as calcium carbonate divided by 17.1 equals grains per gallon. Using the posted averages, 71 mg/L is about 4.2 gpg and 105 mg/L is about 6.1 gpg. [1]
Round only as the equipment requires
Keep the original city or test value, then follow the installed product's instructions for entering or rounding the setting.
Label where the sample came from
A sample before a softener measures feed hardness. A sample after it measures treatment performance. Those results can differ without either one being wrong.
Use grains per gallon for the decision it actually supports
Useful use
Misuse to avoid
Setting or sizing hardness-treatment equipment from a current, relevant input value.
Diagnosing an odor, bacteria concern, corrosion source, or chemical contaminant from hardness alone.
Comparing untreated and softened samples to see whether the unit is reducing hardness.
Assuming a white deposit proves the exact gpg at the tap without a test.
Estimating regeneration demand with the exact softener's instructions and measured water use. [2]
Copying a setting from another home because it has the same city name.