nyonyakay – In addition to the valid points raised by Tess (post 2), the meters that you’re contemplating would be classified as “check meters” (i.e. downstream of the main supply meters) and so Sydney Water won’t read them, and your Owners Corporation cannot legally issue anything that purports to be an account or invoice for whatever water usage they may record.
So as well-intentioned as your motives may be, unless a Multi-Unit Development is provided with pipework to accommodate the separate metering of Lots and means to convey usage data (e.g wirelessly) to a central location at the time of its construction, then the retrofitting of individual meters to those Lots and/or the use of the water consumption data then recorded is not logistically possible.