מים is always plural in Hebrew. In Biblical Hebrew it is very common that plural is replaced with single both with the noun or the verb. Examples:
וַיִּֽחַן־שָׁ֥ם יִשְׂרָאֵ֖ל נֶ֥גֶד הָהָֽר - instead of ויחנו and ישראל (single) instead of בני ישראל
וְהָרֹג בְּשֹׂנְאֵיהֶם חֲמִשָּׁה וְשִׁבְעִים אָלֶף - not אלפים
Similarly "לא היה מים" is identical to לא היו ...
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 ...