It took almost two years to convince me, and I live here. I put a tape on it and it's more like 2.5 feet from the wall. I thought it was someone spilling water, too. But it's always the same spot, always after a very heavy rain (with wind), and last night no one was home to spill anything. Check out the weather channel and see what rolled through Virginia last night! Where would you caulk an exterior vinyl wall. My theories are that the water is coming in though 1) an inside corner (a breakfast nook sticks out the back, the water surfaces about 2.5 feet into the main part of the house diagonally away from the corner 2)through the spot where the bottom of the siding pops into the channel right above the deck at the top of the poured concrete basement wall--maybe the deck/wind combination holds the water against the house or 3) from much higher up, where the nook roof ties into the house. Thanks again for the reply. And yes, nothing on the interior walls either. Hope I've convinced you!