Good news - this one’s pretty clear-cut. The water main is the landlord’s infrastructure to maintain, not yours. You didn’t break anything. The water that leaked out wasn’t water you used - it was water lost because of a plumbing failure. That’s on them.
Most California water companies actually have programs for exactly this situation. They’re called leak adjustments - if a leak happened and got fixed quickly, they’ll often reduce the bill. Usually the landlord needs to submit the repair receipt to apply for it.
So: ask your landlord (in writing, so you have a record) to apply for the leak adjustment with the water company. You shouldn’t have to pay the inflated portion while that’s being processed.
If your landlord pushes back and tries to stick you with the extra cost anyway, you’ve got a solid position. Keep copies of the bills showing the spike, and don’t hesitate to loop in your local housing authority if they won’t cooperate. But hopefully it won’t come to that - most landlords understand that infrastructure failures are their problem to solve.