Well the water itself doesn't have any sugars or proteins like food so microbes aren't consuming it and rotting it. However, that's not to say the chemistry of the water hasn't changed.

　　水并不像食物一样含有糖或蛋白质，所以微生物无法在其中滋生并使其腐坏，然而这并不代表水的化学性质没有改变。