Evaporative deposition

In detail

Water in a domestic supply carries dissolved solids — calcium and magnesium salts above all. When a film of that water evaporates from a surface, the water goes and the solids do not, so they are left as a deposit in the shape of the drop that held them. This is why a surface that was rinsed with clean water still dries marked, and why the mark appears at the end of the job rather than during it. Two trade sources state the same thing from opposite ends. A bathroom manufacturer puts it plainly: allowing water to evaporate on metal will form water deposits, so the technique is to blot dry with a dabbing action rather than to rub. The glass industry's professional pure-water method attacks the other variable, requiring rinse water below 20 parts per million of dissolved solids and stating that tap water is not acceptable, precisely because that rinse is left to evaporate in place. Between them they give the whole answer: either remove the water before it evaporates, or remove the solids before the water does. Nothing about the deposit is dirt, and no cleaner prevents it — drying does.

Why

• Water marks is explained by Evaporative deposition
• Glass cleaner is explained by Evaporative deposition
• Soap scum is explained by Evaporative deposition
• Road salt is explained by Evaporative deposition
• Ammonia is explained by Evaporative deposition
• Rinse aid is explained by Evaporative deposition
• Water-borne film is explained by Evaporative deposition
• Iron staining from water is explained by Evaporative deposition