Troubleshooting Windshield Mister

As is usually the case with new gadgets, I end up learning to operate an accessory when I need it the most. Such was the case the other day when splashback prompted my learning how to use the windshield mister. It looked like all you have to do is lift the right lever to activate the mister. The rear window mister worked when I rotated the knob at the end. Later, when I looked under the hood I saw that the washer reservoir was 3/4 full so I just topped it off, but again the windshield mister doesn't operate. How might I troubleshoot the system to isolate whether it is the pump/motor, switch or one of the lines coming or going? I hope I don't have to take my Prius in for such a pedestrian problem at 3700 miles.