Learn the hardness from supply information or a specific test of the water entering the machine. Keep the value and unit: foam, taste, and clarity are not precise measurements.
Get a value that represents your installation
If you receive water from a utility network, check the report or the provider. A regional map does not replace the supply data for your home. If you use a well, multiple supplies, or water treatment, a measurement from the relevant point may be necessary.
With a home test, follow the sample collection, reading, and scale instructions from the manufacturer. Range strips provide an approximation; do not invent decimals between colors. If the result affects a treatment decision, confirm it with a method of adequate precision.
Compare units before using a chart
Hardness is usually expressed as calcium carbonate equivalent. The Maryland Geological Survey lists these common equivalents:
| Data | Equivalent for this hardness expression |
|---|---|
| 1 mg/L as CaCO3 | Approximately 1 ppm in water |
| 1 gpg | Approximately 17.1 mg/L as CaCO3 |
For example, 10 gpg is approximately equal to 171 mg/L as CaCO3. Do not compare that 10 directly with a chart in mg/L. If the report uses French degrees, German degrees, or another scale, confirm the conversion in the supply or test documentation before classifying the value.
How to use the result
Check the detergent dosing chart and the appliance maintenance conditions. Soft or hard categories may have different limits on a commercial label; apply the scale from the document you are using.
The data helps assess descaling and deposit prevention, but it does not prescribe a fixed amount of additive. If there is pre-treatment, use the outlet result and verify its maintenance.
What hardness does not measure
It does not indicate the amount of sand, iron, total salinity, or the water's safety for health. If the supply comes out brown or has an unusual odor, contact the provider. When you use well water, rainwater, or tank water, also check the conditions of that source; a hardness strip does not solve the situation.
Record the date, sample source, method, value, and unit. If the supply or treatment changes, confirm the data again before keeping the same settings.