I’m sorry, re-reading my comment it comes across very harsh. I didn’t mean that. The government certainly regulates the requirements for water to be considered drinkable. However it is probably not feasible to make all tap water on an island drinkable. Most of the water running through the tap is not consumed (like shower, laundry, flushing, etc.) so it might be smarter to make the water clean enough for those jobs and then advise to consume only bottled water.

Why do you assume mainland tap water and tap water on a tiny island far out in the ocean have the same quality? In spain mainland tap water is generally considered drinkable.

My OnePlus also does that