97 Quest water leaking problem

I purchased my van in june (dry season). We had three days of rain last weekend. My front passenger & driver's carpet are wet. I pulled up some of the carpet and the underlay is also wet. I cannot have the van out of service as I live off a bus route and drive my two toddlers to daycare everyday. I will attempt troubleshooting myself this weekend. Does anyone have any ideas? I am only guessing it is coming up from the floorboards as I have hosed my van often and have not detected wet carpets after. Any easy way of checking?

Check the ac unit for leaks.