it'll make all the chlorine (a chemical) evaporate.
and microbes include algae, maybe that's why he's doing it, to retard the growth of algae... they are aquatic after all.
bringing the water up to a boil should be enough. as long as any liquid reaches it's boiling point, it will not (the liquid) get any hotter.
Chlorine will have evaporated by then (as will alcohol... not that you'd have alcohol in your water, but that's how they concentrate alcohol) and the microbes are small enough that all the heat possible will have been transferred to them by then... but ... well, tell me if i'm wrong... I have a feeling i'm wrong about the microbes and boiling it for a longer period of time would have an effect... anyone know for sure?
edit: I don't think distilled water will boil right? the water needs dissolved gases and impurities to boil. I know it won't boil in a microwave anyway. That's why it's so dangerous to heat distilled water in the microwave- you won't think it's too hot, even though it's superheated, and when you add something to it, it'll explode in your face.