Windshield washer is water, denatured alcohol, and blue color so you know there's something in your reservoir when you take off the cap or look at the side. I don't know the proportions off hand, but I'm pretty sure it's 90+% water and the rest alcohol and coloring, just like anything else you buy pre-made in a store. They're charging a lot for a gallon of water.
The water does the cleaning, the alcohol helps evaporate the water left over so you won't have streaking when the wipers do their thing.
From what I've read here and other places, it's the water that does most of the cleaning. All the components of BP during manufacture are water soluble. All the components of fouling left over from shooting BP are water soluble, the alcohol evaporates the water left over after the contaminants are washed away. Heated water does better because it speeds up the breakdown of the solubles. You don't have to use as many patches if you use scalding water than room temperature water.
Natural lubes mix with the contaminants when the heat of the combustion takes place, so they'e bonded to the water soluble contaminants and makes them slick. If you use a petroleum based lube of some sort, it bonds in a different way, that's why you get hard and crusty contaminants that are hard to get off because they're not insoluble; the water can't flush them away, you have to chip them off with a brass brush or a dental pick.
The substitutes are different than real BP, so they act differently and opinions vary about what's best to use, I don't have the money to invest in the materials to study what Windex with or without vinegar actually does, or the ammonia, and so forth. It would just be uneducated guesses, but I figure the water and ammonia or vinegar do the cleaning and the alcohol helps get the remaining water out.
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