My tenants have reports a sketchy scenario where damage occurred. Am I responsible for repair?

My tenants have reported that a pipe under the sink had come loose and that water spilled onto the floor causing the floor tiles to come up. One even went under the cabinetry and is now out of reach. The loose pipe has been an issue of contention since it is a simple screw tightening setup that I've never had trouble with before. I've repeatedly driven to the house only to find that a simple tightening is all that is required. I'm under the belief the tenants are hitting it with something (stored under the sink) and causing it to come loose. During a visit two months ago I noticed loose tiles and recorded it in a repair journal, but umed that since it wasn't reported that they must have caused the problem (college parties and what not). I had tenantively planned to repair the problem after they move out with the security deposit. The lease states reasonable care must be taken and that all repair requests must be made promptly to the landlord. This is at least two weeks late (by their own admission) and two months late by my own records. Without definitive proof of wrong doing am I responsible to repair something they probably did?