Massachusetts sub meter issues

We wanted to sub meter but the law in Massachusetts doesn’t allow us to bill any of our existing tenants for water usage. I won’t bore you with the law, but it essentially prohibits old parks from charging existing tenants for water. If you build a new park you can do it.

We still have the issue of running off a main and chasing leaks. Tenants run water in winter to avoid paying for heat tape- breaking the lease agreement of course.

We have a Nowi electronic reader on the main which has greatly helped us see leaks in real time. But we don’t know where they are and have 100 units.

What are your thoughts on the most cost effective way of narrowing down leaks. Do I just go with an individual nowi device on each home? Then I at least know where the leak is. Or, is there a way to get Maybe groups of 5 homes put on one sub meter? We have very few curb stops so currently have a hard time narrowing things down without simply walking the park. Thanks for any input you have.