Whale – despair not – it can be done – here’s how.
Don’t ask the owners – just decide to do it – here’s how we did it – the EC decided that as the only responsible body charged with maintenance of the whole of the complex, we would go ahead and get a Sydney Water WaterFix done for the whole of complex.
This cost something like $25 per unit (maybe $220 subsidized value) – we paid from body corporate funds – and got it done by notice/arrangement – coming on these dates, provide access or pay a call-back fee – done and dusted in short time – and – listen to this – payback was 1 month ! – meaning the next months lower water usage bill recovered the cost of the WaterFix. So – get that done first.
Now – recently – we have decided to install individual wireless water meters to each unit. This will be a big cost – around $1500 per unit – and require a special levy – but here’s the beauty – as soon as it is done, owner levys will drop by the amount of the water usage bills, which will then be charged to the previously-wasteful/overcrowding tenants ! 
You can bet that as soon as the tenants get some big water bills – they will very quickly change their habits of long showers and inviting all their friends over for free showers – as they will be paying the water usage bills in future !
I’m guessing the special levy cost will be paid back by the reduced levies the the first year – tenants change and become water-saving conscious, and owners pay lower strata levies – sweet ! 