Most UAE tap water starts as desalinated seawater, which leaves the plant fairly soft, then picks up minerals in the network and, crucially, in your building. Older towers and villas store water in rooftop or ground tanks, and areas that blend in groundwater, notably parts of Al Ain, Ras Al Khaimah and older Sharjah districts, run genuinely hard. Calcium and magnesium ions bind to the negatively charged surface of hair, building an invisible mineral film. That film is why hair here often feels coated but looks dull, why blondes drift brassy or greenish when copper is present in old pipework, and why conditioner seems to stop working after a few months in a new flat.
The film also sabotages chemical work. Keratin and protein smoothing treatments need the product to penetrate the cuticle and bond; a mineral layer blocks that, so the treatment sits on top and washes out in weeks instead of months. A stylist who knows the market will start a smoothing appointment with a chelating or clarifying wash to strip mineral deposits before applying anything expensive. If your at-home keratin quote does not include that step, ask why. The same logic applies to colour: minerals shift how dye develops, which is one reason a good colourist does a strand test with your actual tap water rather than trusting the swatch book.