I noticed one day when it was really cold and raining. My rear window had a lot of water droplet forming. It was odd that I tried to use my rear wiper and the water wasn't wiping away. I opened my trunk and to my surprise a lot of condensation has formed into water droplets on the window. It makes sense now why my cargo cover has water spots on it. I know my trunk doesn't leak cause I washed my car multiple times and no water has leaked. I have never seen condensation form so much on the inside of a window. Is this normal?
The Prius rear window does tend to fog up easily in rainy and/or cold weather. I have never seen water droplets form though. During rainy and cold weather I pretty much keep the front defrost on, mostly by changing the Mode for continuous defrost. If the fan speed is at least moderate it also does a pretty good job of keeping the side and rear windows clear. If not, I will run the Rear Defrost every now and then.
...sounds like you might have too much moisture trapped inside the car...I try to leave the windows open in our garage to give moisture a chance to escape. Can't get my wife in the habit though, and she actually "owns" the Prius in our house.
Condensation happens whenever some surface is colder than the dewpoint (a measure of humidity) of the air. Nothing really to do with Prius, or cars for that matter. In order to alleviate it, you either need to warm the surface, or reduce the humidity in the air. If this happens often, you might look for a source of water in the car. "I know my trunk doesn't leak cause I washed my car multiple times and no water has leaked." You didn't SEE any water, doesn't mean it isn't hiding somewhere. The fact that it is more prevalent on the rear window, might indicate (along with the water stains on the cargo cover) that there is a moisture issue of some sort back there.
