So You Want To Put Plain Water In Your Windshield Wiper Fluid Reservoir?

6 June 2018
 Categories: , Blog


With the push to find more environmentally-friendly -- and more affordable -- options for your home and car, it's no surprise to find people asking about using plain water in their car's windshield wiper fluid reservoir. After all, water doesn't require a separate trip to the store, and you can add it whenever you need to. However, it is really not the best choice if you want to keep your windshield safe and clean.

Off the Hook for a Few Months

In the summertime, and anywhere that you have warm weather that isn't going to drop below freezing overnight, plain water isn't exactly going to harm your windshield wiper system. The really big problem with using plain water is that it can freeze. So as long as the temperatures remain above freezing, that shouldn't be a problem.

But if you're in an area where temperatures can occasionally dip down -- even sunny Southern California and hot Arizona can have freezing temperatures in winter, remember -- then you need to clear the water out of the reservoir. That leads to you spending more money to have a mechanic do it if you're not able to drain the reservoir yourself.

And you can't simply fill the reservoir with commercial wiper fluid once winter hits -- you have to get all of the remaining water out.

What It Really Cleans

Water is effective for moistening and washing away dirt. But it's not that good for washing away pollen stains, bird droppings, dead bugs, and other materials that end up on your windshield. That's why those window washing buckets at the gas station have detergent in them, and it's why commercial wiper fluid contains a bunch of ingredients that cut through gunk much more quickly than plain water would.

Plain water can also leave streaks. Because it doesn't clean away gunk as effectively as commercial fluids, you have bits of that gunk left over on the glass. Those can dry into streaks and scattered blobs.

And Then There's the Rest of the Car

If you're thinking to yourself that you can drain out water and will be OK with a few streaks, there's one more issue that should warn you off using plain water: Legionnaire's disease. When that water sits in the reservoir, next to a hot engine on a warm day, any bacteria in the water can multiply like mad. In regions where Legionnaire's disease is a concern, that means the bacteria that causes the disease can increase and infiltrate the engine -- and thus the filtration system.

The BBC reported in 2010 that of cars tested for bacteria (as part of a study to determine why long-distance drivers had more disease risk), none of the cars that had wiper fluid had bacteria -- but 20 percent of the cars that used plain water did have the bacteria.

So if you've been thinking about adding plain water, don't. And if you already have, contact an auto repair shop like Hillis 66 Service to have the reservoir drained and filled with commercial fluid.