I've had a few tenants that allowed water to run non-stop in a multi-family property. I also had clients with the same problem.
As an Owner, Manager or State Licensed Plumbing Contractor, I am allowed to ENTER A UNIT in CASE OF AN EMERGENCY. A "possible" constant water leak can be classified as an emergency. Water can destroy property and lead to Mold issues.
So what I've done as the owner, manager and licensed plumber is:
a) Post a notice on every tenants front door that there is a plumbing leak and I plan on entering their unit to investigate. This may occur from 12:01 AM through 11:59 PM, any day or night for the next 30 days!
b) I show up with my stethoscope to listen to water flows in a pipe, keeping a log of who's using water in a specific area (kitchen or bathroom).
c) I also take my digital camera and take a time/date stamped picture of the water meter, is has a flow meter too so I can see if water is beings used.
Then each time I've detected water being used, I document by photo how much water is being used at any one period. A bath should use less than 50 gallons. A long shower less than 25 gallons, and so on..
As after I locate the water being used (with my stethoscope), I will knock on the tenants door, then let myself inside. I take pictures of the water flowing from a faucet -- proving the tenant is wasting water.
Then I can alert the Utility and my Cities water conservation department. Also with my attorney's help, I can file a complaint, lawsuit or begin an eviction.
In only One case, I proved a tenant was allowing the bathtub to run at full force for 30 minutes each day, costing me around $225 a month in extra fee's. I was able to evict and got a judgement for the extra water usage.
Collection was another story.. --47.155.xx.xxx