Are you sure it is water? Give it a smell, if it smells sweet, it is most likely coolant, which can leak into the passenger side footwell because the heater core is mounted in the dashboard on that side. If it is a leaking heater core, it is a pretty involved repair that involves removing large amounts of the dash. If it is, in fact, water, I would go to a self serve car wash and try to look under the dashboard while someone sprays down the passenger side of the windshield, hood, and door.