Q: Water under passenger seat and mildew problem

While driving in the rain one day, with the A/C on, I noticed a lot of cold water under the passenger seat. Under each seat in my car, there is a very flat hose, which I assume is to vent air to the back seat passengers. I thought that the water condensed and leaked out under the passenger seat, but the dealership is totally stumped! They’ve checked everything that seems relevant, including the evaporator coil, but that’s not it. They couldn’t duplicate the problem. They could not find a way to help me and now I have to live with Mildew in my car! Please tell me what to do and how to find help for this problem. Thanks.