I have used ID78 as a Neutol-WA replacement on and off for some years. I have never used EDTA, nor seen the need for it and I'm on the same water supply as yourself. Melbourne's water does have some issues, usually around March after a long hot dry summer. The various reservoirs may have a flocculent added to the water around that time in order to drop precipitates to the bottom of the reservoir if they are running low. Even then the Melbourne water is pretty good.
I haven't noticed much if any difference over the 2019 - 2020 years after the drought then bushfires, followed by the floods. The input of de-salinated water in ever greater amounts over the entire reservoir system during that really dry period also didn't seem to make any difference, but this is only going on print output, not scientific measurements. This year the water seems really good, which, when one considers the amount of rain we've been having, is pretty good.
I generally mix 2.5 litres and use my Durst Printo processor so I have super consistent temperature control, which is another parameter taken care of. I run the bath at 25ºC for completion of development certainty in 45 seconds. I generally dilute to 1:1 for higher contrast, although there is some loss of warm tone strength at this dilution, it suits me.