Does water in your lawn mowers gas tank hurt the lawn mower?

Yes, water in the lawn mower gas tank can hurt the lawn mower. Water in the gas will make it run rough and any water left in the engine when it is shut off can cause rust on the pistons. Good new is that if the lawn mower still runs you can dump out the old gas and put in new gas and the lawn mower should be fine. The rust will wear off in time.