Twice, I have had a water bill 10 times my normal usage. (Both times the culprit was an in ground irrigation system.) Our local water authority will "forgive" up to 50% of a high water bill if you document to them in writing the root cause of the problem and show them a receipt for what you did to fix it. So appeal to them. They may be sympathetic.
If they're tough with you, demand to know how much water THEY lose through leaks in their distribution system. The amount is probably shocking. Read this if you want to get pissed off:
As Infrastructure Crumbles, Trillions Of Gallons Of Water Lost : NPR