Dripping water in the passenger side of the cockpit was a very common occurrence in Alfa 164's (1991-1995). The biggest culprit was a condensation drain pipe that routed the water from the evaporator, out the bottom of the car (this is why on cars with A/C, you'll always notice a puddle of water under your car). Anyhow, this little drain pipe was notorious for becoming clogged. Since the water couldn't drain, it would overflow the evaporator box and dribble into the passenger side footwell.
All you had to do was push a wire (coat hanger) up through this little drain hose to clear out any debris. Water would then flow out like the mighty Mississippi!
A quick look at the Maserati parts manual shows the cars do have a rubber drain tube. My guess is that if you crawl under the car and look for it, it will be clogged with leaves, debris, etc....