Water leak issue

[Cydney Smith]

On the 2nd of January, 

Our tenant called and said there was a water leak in front grass area of yard that she thought was an irrigation system leak. We instructed her on how to turn off system and requested se let us know if leak continued

(we are in Missouri .. rental is in Florida..)

A week later we called her and she said it was dry  .. 

on January 17 tenant called and said the city called her to report heavy water usage. 
my husband (a plumber) drove straight to Florida and upon inspection found a stress break in pvc pipe on main water line that goes into house (located the break under grassy side yard ) He said that kind of crack was from a heavy vehicle parking or running over that area. Florida code doesn’t require deep install like Missouri does.. 
He then went to the city utilities and found that the water bill was $950 twice what it had been the previous month .. tenant had her family come for holidays and there is no parking on the street .. and our lease clearly states no parking on the grass .abs property is rented as is. . City will credit 50% of overage after 6 months of average usage determination.. Are we responsible for paying the difference or is the tenant? Never had this happen before.. We want to be fair but this tenant clearly stated it was dry 10 days ago .. Any advice out there is greatly appreciated!