It sounds like the kitchen sink drain pipe became detached somehow. A somewhat unusual event, unless some activity was being undertaken in the area of where the disconnect occurred. Even then, the connection should be sufficiently durable to withstand some bumping, jarring, or whatever.
However, as scylla has said, if the disconnection occurred without any fault on the tenant's part, then it should fall under the landlord's obligation to repair and maintain the premises.
I disagree with Qwertypod's view that "Landlords are largely responsible for appliance repair, not leaks." They are responsible for both, if there is no fault (including negligence) on the part of the tenant. For example, let's suppose the washing machine in the rental premises decides to spring a leak, from old age, some defect in the machine, or whatever. Taken at face value, under Qwerty's regime, the landlord would repair or replace the machine and the tenant would pay for the water damage caused by the leak from the faulty appliance, even if the tenant did nothing to cause said leak. That seems hardly fair or just.
Assuming the tenant has insurance that would respond (as in the case of most tenant policies), that insurer would likely appoint an adjuster to investigate the loss, and the insurer would likely deny coverage if it formed the opinion that there was no liability on the part of the tenant. In any event, even if the insurer would agree to accept the claim, the tenant should be slow to claim under his/her policy. One does not want to find oneself with any kind of a record of making claims. That can lead to two undesirable consequences: (i) an increase in future premiums, or, worse (ii) a denial of future coverage.
If the L/L claims under the L/L's policy, its insurer will also likely investigate and make at determination as to whether the loss falls within the L/L's coverage. In many cases, where both L/L and Tnt. are insured, both insurers become involved and seek to agree on which policy should cover the loss. If I were the landlord and I thought my insurance should be the one to pay, I probably would not claim unless the quantum of loss was high indeed. Better to simply self-insure against small losses and save making any claim for something major.
Taking me as an example, on both my home and on a rental property, I have sought and obtained a policy deductible of $10,000, even though, for a higher premium, the deductible would be only $1,000. Frankly, I would rather cover a loss of $10,000 out of my own pocket than find my insurer deciding to dump me at policy renewal time. It happens. I want coverage if the place burns to the ground and I am facing a million dollar loss. Replacing a kitchen floor I can handle.
