Possibly, yes — if there’s a proven defect that you neglected to fix and that directly caused the fall.

I own a unit on the second floor. 5 days ago, my tenant apparently left the kitchen sink on and caused flooding.

Water can be tricky if not dried out quickly which can cause a lot of other problems. 

But the unknowns around it can be.Moisture = Symptom, Not the ProblemYou’re right to focus on not knowing the cause.

I often see investors struggle with city permits and drawing requirements which cause costly delays.

Google says 1/2% is normal, 5% might be common, 12% is the upper limit of acceptable and 17% is a cause for concern.

Quote from @Sami Gren: Quote from @Drew Sygit: Tenants ALWAYS want what is easiest for them.Unfortunately, as others have pointed out, messages sent via random channels can actually cause chaos.Structure is needed, which a percentage of tenants will NEVER like:(We only allow emergency issues to be done via phone or SMS - known as "blood or flood" in the industry.

Insuring the property under your LLC while the loan is still in your personal name can cause issues with your lender.

We also define an emergency as something that will immediately cause an occupant bodily harm or damage to the property. 

In my opinion your friend might have a cause of action for equitable improvement, but the possibility for success depends entirely on the specific facts.