What can I do if upstair tenants maliciously running up water bills

[Qingxuan Zhou]

I am living in a triplex, I have this nightmare upstair tenants for about one year. And recently their landlord finally sent out lease termination notice to ask them to move out. And "coincidently" the daily water usage jumped up 10-fold, from 60 cu.ft per day to 600 cu.ft per day EVERY SINGLE day!! I could hear water running sound from above non stop. I requested the association to send plumber to investigate all units. But, if it is not a severe water leak but caused by those tenants, I desperately need alternative suggestions here. Also the association is at the same time that landlord.