From "Bushwalker's Business" cited above, I understand that the source of the pollution is an uncapped coal mine within the NP precinct, which has been continually gushing zinc-contaminated water into a tributary of the Grose.
Filtering won't work - you can't filter out dissolved metals (btw, I don't think Zinc is a heavy metal.) Boiling won't work. There's nothing you can do to remove the zinc if you're planning to drink it, except perhaps find something which will chemically combine with the zinc to form a non-soluble precipitate, then filter ... good luck finding something less toxic than the zinc you're trying to remove ... I dunno anything about chemistry.
BTW, from aforementioned chapter in cited book, they went looking for this pollution after surveys of the river showed a significant reduction in the number and diversity of invertebrates (like dragonfly nymphs) below the junction of the creek contributing the pollution; and yes, the sewage treatment works actually *decreased* the pollution of the Grose.
Read the book, it's quite good.