Water leak tenant told me after it was leaking a month

[Sherry Woods]

We have a tenant that told us there was a running toilet a month after it started to leak. The water co says that it started 4 days after they moved in but they did not tell us for a month.  Now she has a $500.00 water bill.  We had a plumber repair it, but it took him 3 more weeks to repair after she told us. Who is supposed to pay landlord or tenant?