Question: "My car doesn't seem to leak when it rains, but afterwards when I drive around a corner, water pours out from the side of the dashboard onto the floor on the passenger side."
Answer: Many cars have a tray below the windscreen which often contains things like the windscreen wiper motors, water from the windscreen often runs through the scuttle and into this area which should have at least two drainage holes, possibly more. The problem is that this area can typically get filled with leaves and debris, which block up the drainage holes over time and fill the tray. It can then slop from side-to-side, front-to-back while you are driving and slosh over into holes in the bulkhead and pour down behind the dashboard. The solution is usually just to unblock the drainage holes, although some sealing of the bulkhead can also prevent future leaks.