Ammonia is very close to water on a molecular level, and it mixes instantly with water. I thought Windex had ammonia in it, but I now realize it does not. Regardless, I know that I am a klutz, and if anything can go wrong, it will, and if I use Windex, it's just a matter of time before I dump a whole bottle in a sump. So I use what my mother used for windows; 1/2 distilled water and 1/2 distilled white vinegar.