this is why a lot of folks suggest vodka or sanitizer in the airlock. Your situation will likely be fine if you got the water right out of the tap into the airlock when you filled it. I.e, it wasn't exposed to anything on the way. I once got a teensy bit of water that had been in the sink in my yeast starter when the starter tipped over. Ruined a whole batch of beer and my best guess is there was something on my nasty sink that got into the water and then into the starter. Again, though , most likely your beer will not be affected by a little bit of airlock water.