According to my lease, I pay a fixed monthly price for the water bill.
My landlord complained that the most recent water bill was significantly higher than it had been in the past. He inspected the apartment and discovered that the handle of the water release of the toilet was malfunctioning, causing a major water flush. When I apologized for my procrastination, saying that I’ve known about that issue for some time, he demanded that I pay the extra amount, since I neglected to alert him to repair the leak.
I checked my contract, and it does not stipulate that the tenant is liable if he fails to inform the landlord in such a circumstance.
Q: Am I obligated to pay my landlord the difference of this month’s higher water bill?
A: Although you did not damage any property, your negligence to inform the landlord of the leaking toilet indirectly caused him a loss. Hashavas aveida, the Torah’s obligation to return a lost object to the owner, includes an obligation to prevent someone else from loss. For instance, one who sees water threatening to flood a friend’s field is obligated to erect a partition to prevent the field from flooding (C.M. 259:9).
If, despite the Torah’s obligation to return a lost object, one fails to do so - thereby violating the prohibition against turning away from a friend’s lost object - is not obligated to reimburse the owner for the object. Liability occurs only if one did or said something that caused an object to be destroyed; someone who merely neglected to return an object is not liable (Ketzos 66:21). As such, it seems that your landlord cannot demand that you pay the extra cost of the recent bill.
On the other hand, one who neglects to return a lost object must discharge a halachic moral responsibility (latzeis yedei shamayim) and repay the owner of the lost property. It is similar to a case of two witnesses who, by refusing to testify, are causing a litigant a loss and must repay the litigant that lost money, latzeis yedei shamayim (Gilyon Maharsha to Shach C.M. 259:1, Minchas Shlomo 1:82).
This principle applies to your case as well. Your negligence to inform the landlord about the malfunctioning toilet caused him a loss. As such, you have an obligation latzeis yedei shamayim to discharge this responsibility.