Possibly. Fortunately I've come up with a simple test to tell the difference between water and alcohol. Methanol is poisonous so you can't do a drink test, and food coloring can easily trick people, so it comes down to fire. Methanol is flammable while water is not. To tell whether or not you were ripped off at the store, all you need to do is check if your washer fluid readily burns.
I've created a video to show this effect. Very similar to ethanol, methanol has a very faint blue flame. It's difficult to see, but it's definitely there.
http://www.youtube.com/watch?v=DOV46WypxkA