Well then maybe you should make them sue you ! first here it might help you to know how often the city issued the water bills ? meaning is the LL claiming that this leak caused 3,000 .00 in bills for one billing period ? I doubt it but anyway there is no logical reason that they could not have found the leak sooner if they claim 3000.00 in one billing period, Ill lay odds that this toilet could have caused a 200.00 to a 400.00 increase if the bill was quarterly BUT not 3k and if the LL is attempting to get more than on billing period of use here they really need more proof like submetered readings ,Call that cities water dept and ask them in dollars approximately what a leak could cost per billing period ( and if they bill monthly or quarterly) Now so you know just because the lease said the LL was to pay that utility does not mean that a tenant can allow it to be wasted and yes with 4 apartments at any given moment it is impossible with out sub meters to individually show which apartment has used how much then the LL has to rely on other things but I would argue that simple video is not enough to justify 3k, this landlord can threaten eviction but courts are the ones to evict tenants and LLs options are to send notice to tenants telling them that they believe they have violated a lease and want the tenant to move out or they can choose to not renew a tenants lease and make sure the tenant has proper notice telling them to move out. ( don't be surprised if your mom still must move out due to LL refusing to renew) SO how long does the LL claim this went on ? if they had said anything about how long they think it went on ?