You've likely got a blockage in the plenum area under the bonnet, this is causing water to enter the cabin, collect under the front passenger seat and begin to ruin the convenience module that sits under there, get the carpets up and check the sound deadening isn't full of water.
IF the CCM goes it's £££'s as by that time the wiring has corroded away too.
Check under the battery and behind the servo, there are drain plugs there that will be blocked up with all sorts of ming. Also check the seal on the pollen filter housing, that can leak too.