Washer fluid can be tap water, mix with some household cleaning agent till washer fluid produced for the vehicle. It is not the same as the coolant in the car radiator that we should not fill with tap water as it could cause corrosion to the parts in the long run.
You can use tap water as the windshield fluid even it may not have efficiency enough to eliminate the bug, mud, or stubborn dirt on it. It will be a problem of freezing when you use a car in cold weather also.
Washer fluid has the particular formula solutions to get rid of quickly the stubborn dirt, bird dropping, and antifreeze on a car windscreen.
Methanol alcohol is an important one of its formula. Besides flammable, it is well-known as a dangerous chemical solution to humans, wildlife, and the environment. Washer fluid manufactured more than a billion liter per year around the world.
Its poison causes environment contamination and illness in people when they swallow, such as dizzy, vomiting, sleepy even cause of death. That’s why European countries banned Methyl alcohol in washer fluid over ten years ago.