Builders, chelators and hard water

The invisible ingredient, and the reason a formula that works in one place disappoints in another.

The problem hard water causes

Hard water carries dissolved calcium and magnesium. Those ions react with anionic surfactants and precipitate them out as soap scum, which is both the white film on a shower and the reason the cleaner stops cleaning.

The surfactant consumed by hardness is not available to lift soil, so a formula that works in soft water underperforms in hard water at the same dose.

Builders

Materials that sequester or precipitate hardness ions so the surfactant is free to work, and that raise and buffer pH.

Sodium carbonate, sodium citrate, silicates. Phosphates did this best and are restricted in many jurisdictions for environmental reasons, which is why modern formulas work harder at it.

Chelators

Molecules that bind metal ions specifically and hold them in solution.

They do three jobs at once: free the surfactant, stop metal-catalyzed degradation of the formula, and improve the performance of a preservative, which works better without free metal ions around.

EDTA is the traditional one and is under environmental pressure; GLDA, MGDA and sodium gluconate are the usual replacements and are what a maker wanting a defensible green position should be looking at.

Why the formula stops working in one region

This is the practical reason the page exists. Water hardness varies enormously by area, and a customer diluting a concentrate uses their own water.

A concentrate developed and tested in a soft-water area will underperform in a hard-water one, and the complaint will read as the product being weak rather than as a water problem.

The defenses: build enough hardness tolerance into the formula, use nonionic surfactants which are far less affected, and test with deliberately hardened water rather than with whatever comes out of your tap.

References