Iron staining from water
Water itself carrying the stain. Above three-tenths of a part per million, the supply is the source of the mark.
In detail
Iron dissolved in a water supply deposits as it evaporates or oxidises, leaving orange to brown staining on whatever the water last touched. A public-health cleaning guideline puts a number on it: above 0.3 parts per million, iron in process water is listed as a cause of STAINING. What matters about iron staining is diagnostic rather than chemical. A reader who finds recurring orange marks in a basin, a toilet, a dishwasher or on laundry generally treats them as dirt and then as a failure of their cleaner. If the water carries iron, the mark returns after every clean because the supply is depositing it again — and the fix is water treatment, not a stronger product. Stainless steel left wet can discolour for the same reason: water may contain iron, and drying is what prevents the deposit.
Why
- Iron staining from water is explained by Evaporative deposition
Sources for this page
Sources
Dairy Processing Plants: Guidelines for the Cleaning of Dairy Plant Processing Equipment
British Columbia Centre for Disease Control (BCCDC), Canada · Government or regulator
Relied on for: That Table 4 sets maximum water concentrations of 500 ppm total dissolved solids, 0.3 ppm iron, 250 ppm chloride, 0.2 ppm manganese, 10 ppm silica, 3 ppm copper and 250 ppm sulfate, with the concerns filming, staining and corrosion. (states this directly)