Don't refill your windshield washer with plain water if you live any place that can see freezing temperatures. Even doing so in the summer can be catastrophic if you forget to switch the fluid for real stuff before winter. A frozen windshield washer system can crack your fluid reservoir, ruin the electric pump, crack all of your washer hoses under the hood, and even crack your plastic windshield sprayers. This can add up to be a very expensive repair. Don't forget you may have a washer for the rear window, too!