Many drivers prefer to make their own windshield wiper fluid instead of buying at the store for two reasons: first, it's cheaper to make your own fluid, as store-bought fluid often costs $3 to $6 for a single jug. Secondly, store-bought wiper fluid contains harsh chemicals that are bad for the environment. If you're thinking about making your own, keep reading for a step-by-step walkthrough.What You'll Need Water (preferably distilled, not tap)Empty jug (1-2 gallons should suffice)Dawn dish soapAmmonia or vinegarBlue food coloringHow to Make Wiper FluidOnce you've acquired the necessary items, it's time to get started. Take the empty jug and fill it 3/4 full of water. Next, add 1/2 cup of non-sudsing ammonia or vinegar (either or which are acceptable), a few drops of blue food coloring, and 1 tablespoon of Dawn dish soap. Stir the mixture until all of the ingredients are evenly distributed, at which point you should be good to go!The blue food coloring doesn't serve any functional. Rather, it reduces the risk of other people or animals ingesting the solution. The ammonia -- and certain types of dish soap -- are not safe for human consumption. By dyeing your wiper fluid blue, you and others can identify it more easily.It's also recommended that you use distilled water since it doesn't contain trace minerals. Tap water -- even if looks clean and clear -- contains small amounts of chlorine, iron and other impurities. Over time, this can lead to mineral deposits on your windshield and within the reservoir tank and lines. Opting for distilled water, however, prevents this from happening.Pop the hood of your car, locate the wiper fluid reservoir, and pour your newly created wiper fluid until it reaches the "max" line.What About Store-Bough Wiper Fluid?Store-bought wiper fluid isn't necessarily bad, assuming you choose the right type and use it as directed. It's not uncommon for store-bought wiper fluid to require dilution with water before filing it in the vehicle's reservoir. So, read the instructions to see whether or not you need to dilute it, and if so, how much water you need to dilute it with.Some store-bought wiper fluid is also designed for specific seasons, such as winter or summer. When switching from a summer to winter formula (or vise-versa), drain all of the remaining fluid from your reservoir before adding the new fluid.