Yes, you can retro-fit but then you have to decide who’s going to read them. If you want every apartment to have a meter and then have it read by the water supplier, it’s going to possibly create some access issues. If you want to have the meters installed on a voluntary basis with those who opt in charged for actual water use by the Owners Corp and those who opt out charged on a pro rata basis, then access isn’t so much of an issue as anyone who has ameter would be happy to let it be read.
By the way I heard someone from Sydney Water tell a conference last year that the wireless meter readers aren’t yet 100 percent reliable.