I have door/window sensors running using interruptions. I got rid of the regulator and the power led and I am using a step up converter to take as much juice as possible from the batteries. The oldest node has been running for a year already on 2 AA batteries so your project is definitely doable.
The problem could be in case the leak sensor throws a lot of false positives in which case it would drain the battery quicker.
I hope it helps.