I spent some time thinking about this about a year ago, primarily using Palmer’s “How To Brew”. I too do BIAB, for around 20L final volume. Here's my summary (which is pretty similar to what's stated above).
ACTEW provides water quality statistics buried in their “publications” section of the website, but the table above provides the relevant numbers – Canberra water is low in most of the relevant ions, but does have a fair amount of chlorine.
The principal reason for removing chlorine is that it can result in medicinal flavours. It’s important to remove this pre-mash as the chemical reactions can happen in the mash itself. [topic='64057']Combined wisdom[/topic] of AHB is that the best method for removing chlorine is just to bring the water to the boil.
For a number of reasons, Palmer suggests a minimum of 50 ppm calcium in brewing water, whereas Canberra water generally has around 15 ppm Ca. As mentioned above you can use calcium sulphate (gypsum) or calcium carbonate (chalk) for this. I’ve only ever used gypsum though. Going through the calculations, it works out at about 2 tsp gypsum in 38L water (total water for 20L final volume).
Canberra water is also quite low in bicarbonate, which is great for light-coloured beers, but can result in too low a mash pH for dark beers. Adding sodium bicarbonate (baking soda) can fix this. My calculations work out at about 2 tsp bicarb in 38L water for stout, half that for brown/copper coloured beers, and none for yellow/golden colours.
But, both of these additions are almost certainly not needed for making most beers with Canberra water.
Hope that helps, and I’m more than happy for any constructive criticism on this!