In regards to treating water....
There are two forms of water contamination you need to be aware of - Biological, and Chemical (or inert). Purification tablets, filtering, boiling and UV treatment all deal with organic contamination - bacteria, virus, protozoa, amoeba, parasite eggs etc (with some variations in effectiveness) - however they do nothing to mitigate the chemical - heavy metals, pesticides, inorganic fertilizers, industrial oils, "forever chemicals" etc etc. (eg see
https://www.theguardian.com/australia-n ... ntains-epa ).These chemicals could, at any time, be in suburban run-off - there's no practical way of testing while bushwalking - so you really just have to check your maps, and if there are streets/houses/factories/businesses and so on upstream, don't drink it at all. This would include Leura Falls Creek, Jamieson Creek, Katoomba Creek, Kedumba River, Govett's Creek - and of course nearly all streams in the Sydney Basin. Other streams that drain from bushland only - eg. Waterfall Creek, Cedar Creek would generally be OK to purify - but even then, there can be unknown contaminations, for example heavy metals from mining (though in the Blue Mountains this risk would be pretty low, except perhaps around active mines near Lithgow.)
Most of the time, those inorganic contaminants will be in such low concentrations that even if you consumed one or two litres from the stream, it's effect on your health would be minimal to zero - but you just don't know. In an emergency, if you're desperate for water, you'd take the risk, but normally you'd try to plan not to have to.
Take care,
Skibug