Dilution is not weakness

Detergents work by surrounding grease with molecules that have a water-loving end and an oil-loving end. Once there are enough of them to coat what is there, adding more achieves nothing — the surplus has nothing left to attach to and simply stays behind when the water evaporates.

That surplus is the dull film on a glass, the streak on a window, the stiffness in a towel and the loss of absorbency in a microfibre cloth. It also attracts dirt, so an over-dosed surface gets dirty faster than a properly rinsed one.

Dosing instructions are written for average hardness and an average load. In a soft-water area you can genuinely use less than the packet says; in a hard-water area the extra is being consumed by the minerals rather than by your laundry, which is a different problem with a different fix.

The rule of thumb worth keeping: if a surface needs rinsing twice, the mixture was too strong. Weaker and longer beats stronger and faster nearly every time.