If a gentile boils non potable water (water that can't be consumed without being boiled), does such water have a status of Bishul Akum? Is water fit to be served by a King's table?
In general there is no prohibition of bishul akum with water since its form and taste do not change through cooking. Star-K for instance writes
Foods whose form and taste do not change through cooking. This applies even to food that would normally not be eaten without cooking (e.g. pasteurized milk or distilled water).
However, if all people would cook the non-potable water you discuss, its din might be stricter. R Moishe Dovid Lebovits writes (p. 19)
In Eretz Yisrael many people do not drink the water without cooking it first. If a non-Jew cooked the water one may still drink it since most people drink it without cooking it first. In other areas where all people cook the water first the din may change, if it is cooked for taste.
However Tosfot (Avoda Zara 31b) argue that beer is not subject to bishul akum because it is not proper to serve it to a king. One could argue that boiled non-potable water is in the same category and that kings drink mineral water (see here).
I discussed the above with R Binyamin Tabady who concurred based on the last argument.