Water leakage in basement

[Amy Zhang]

I have a rental in NYC.. there is a water leakage in the basement... it only leaks around 4pm or 10pm at night.. plumber/ contractor is not able to find where the water is leaking... he thinks first floor tenants are pouring water down on purpose but not sure where they are doing that from.... Any suggestions? Cannot evict tenants during COVID 19 and it’s also hard to evict tenants in NYC... I don’t think it’s legal to place a camera inside...I am not sure what to do... any suggestions would be appreciated