"We could have made water undrinkable. Then why don't you thank Allah?"

أَفَرَءَيۡتُمُ ٱلۡمَآءَ ٱلَّذِى تَشۡرَبُونَ (٦٨) ءَأَنتُمۡ أَنزَلۡتُمُوهُ مِنَ ٱلۡمُزۡنِ أَمۡ نَحۡنُ ٱلۡمُنزِلُونَ (٦٩) لَوۡ نَشَآءُ جَعَلۡنَـٰهُ أُجَاجً۬ا فَلَوۡلَا تَشۡكُرُونَ

Then tell Me about the water that you drink. Is it you who cause it from the rainclouds to come down, or are We the Causer of it to come down? If We willed, We verily could make it salt (and undrinkable), why then do you not give thanks (to Allâh)?

(Qur'an 56:68-70)