thats the reason most cars have plastic sheet beneath their engines.
secondly in imranbhatti's Fiat, water also comes inside and visibly seen on wet carpet. we have several times discussed this issue but were unable to get ti resolved.
once i drove my diesel charade in rain infact very high level of water. and after couple of days its clutch plates were not working, car was moving if in gear with full clutch pressed. so had to change it. avoid going in deep waters though diesel car does not shut off but still its bad for its health.