Water Hardness and Cleaning Performance

What it is

Water hardness is the amount of dissolved calcium and magnesium. It is reported as milligrams per liter (mg/L, about the same as parts per million) or as grains per gallon (gpg), both expressed as calcium carbonate.

1 grain per gallon = 17.1 mg/L.

How it affects cleaning

• Surfactants: hardness minerals react with many anionic surfactants. Less surfactant is left to clean, and the reaction can form a sticky scum.
• Spotting and film: minerals stay behind when water dries, leaving spots on glass, stainless steel and floors.
• Scale: hardness builds up on fixtures, in dispensers, auto-scrubbers and carpet extractors.
• Floor finish: hard water residue can cloud finish and interfere with bonding of new coats.

Hardness classes

The USGS uses these classes:

How to check

• Ask the local water utility for its water quality report.
• Use hardness test strips or a drop-count titration kit at the tap.
• Check the water after any softener, since buildings may have mixed supplies.

What to do

• Choose cleaners with builders or chelants that tie up hardness. See Surfactants, Builders and Solvents.
• Use nonionic surfactant products where water is very hard.
• Use softened, deionized or reverse osmosis water for final rinses on glass and for spot-free results.
• Use an acid cleaner or descaler to remove existing scale, following the label.
• Rinse floors well before applying finish.

Key points

• Dilution charts assume typical water. In very hard water, follow the maker's guidance rather than adding more product.
• Hardness can change by season and by supply source.
• Hot water does not remove hardness; heating can increase scale.

Common mistakes

• Adding more cleaner to fight spots, which adds residue.
• Using an acid descaler on marble, terrazzo or other calcareous stone.
• Blaming the cleaner for streaks caused by hard rinse water.

Governing standards: USGS water hardness classification; the cleaning product maker's label and technical data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.