Being a window cleaner in Perth I have seen many windows and balustrades that are heavily stained by ‘hard water’, ie water that has a high mineral content.
Although the quality of water in Perth varies remarkably depending on which suburb you live in, Perth water is generally considered to be ‘harder’ than average. In the northern suburbs the local tap water often measures + 450 ppm (parts per million) using a simple TDS (Total Dissolved Solids) meter. Leaving water with this level of contaminants on your glass not only detracts from its appearance but these minerals can stain and even damage your glass over time! I have seen glass less than 3 months old that was heavily impacted by hard water stains.
Spraying your balustrade with tap water after swimming in the pool is a good idea only if the water is pulled from the glass using a traditional squeegee or wiped dry with a microfiber cloth. Otherwise, you are potentially removing one problem (ie the pool water) but adding another (ie the hard tap water). Simarly, rinsing off a window becuase of a faulty irriagtion system is only beneficial if the rinse water is removed from the glass, unless of course one is using ‘pure’ spot free water.
Nanoparticle spray products claim they protect glass from etching. Importantly, windows treated with these products also need to be cleaned regularly in order to retain their appearance.
In conclusion, whether your glass is treated or not try not to leave tap water sitting on your glass to dry. In any case, regular, professional cleaning provides the best protection against hard water stains.
