The usual problem is there's a build up of dirt and other krud in the air
channel in front of the windscreen that's blocking the drain hole, so water
builds up. Fix it by ...

1. Remove the wiper arms
2. Remove the screws / clips holding the air channel cover intake grill.
3. Remove the grill
4. Empty out or suck out the water sloshing around in the channel. At the
lowest point, there's a hole that drains through a rubber hose or other
channel, down to the road.
5. Straighten a coat hanger and CAREFULLY poke down the hole. The bottom of
the hose is usually moulded as a pinch closure, and after a while the rubber
sticks together.

6. Dry out the channel area and make sure there's no rust developing. If
there is, treat it now.

7. Put it all back together.