Hi Dr,
I'm in Epsom and searched the Coliban site a couple of years ago and found the 2012/2013 annual report which had all their water quality results taken quarterly for the year. The later annual reports don't include the water quality data now. The results were similar to the December values you are showing, and not near the other three and were reasonably consistent for Bendigo North and South, Epsom/Huntly and Strathfieldsaye.
The numbers I took from the report are as follows:
Ca 28, Mg 13.5, Na 18, K 0, SO4 4.0, Cl 35, Alkalinity 70