Jef
I’m presuming that the 10 units with own meters are billed for their water consumption directly to each owner, based on meter readings. That means that the remaining 9 are billed to the owners corporation. Your new strata manager is correct in that the cost of the water should be recovered in proportion to unit entitlements rather than equal proportions from those owners connected to the common meter. I don’t know whether you need a special bylaw, if it’s put forward and accepted it would do no harm but if rejected it may be necessary to approach NCAT.
Dave