I had an answer all lined up for this … until I got to the line about being in SA.
If you were in NSW, you’d be allowed to bring in a by-law limiting the maximum number of residents to two adults per bedroom.
Now, it might be interesting to get a copy of the tenancy agreement for the unit, as that might specify how many people are allowed in it. And if the tenants are in breach of their rental agreement, they could be in breach of your by-laws
Also your DA for the block might say how many people the unit is designed to accommodate, although that would be harder to argue in a court or tribunal.
You could try to amend your water levies or contributions to reflect the number of residents per apartment, However that would require a unanimous agreement at a general meeting, according to this handy guide.
By the way, under SA strata law, a unanimous agreement is one where a vote at a general meeting is passed unopposed. So you don’t need everyone in the scheme to agree and you don’t even need everyone at the meeting to vote in favour – as long as no-one votes against.
If the owner of the unit is an absentee, you could sneak the new regulation into the AGM agenda (by using non-alarming language) and they might not even notice if they don’t attend the AGM.
Or you could install separate water meters for each unit and charge the residents accordingly – whichj is a good idea anyway.
The opinions offered in these Forum posts and replies are not intended to be taken as legal advice. Readers with serious issues should consult experienced strata lawyers.