When she gets home take her out to dinner at a very exceptive one at that and say I'm sorry but I have to leave you before you see our basement. pay for dinner and drop her off at the house stay in a hotel. By the way you have to have a suitcase packed in the trunk of the car. leave her a note explaining that you will never flood the house again to do so you are going to have the ro unit mounted in the basement permanently. You can run a 1/4" line upstairs from the RO unit with a shutoff valve on it.

Bill

P.S. if she finds where you are before she calms down you are dead or she is a very forgiving women and then you want to make sure you keep her.