THERE ARE GENERALLY 2 KINDS OF WASHER FLUID AVAILABLE:
THE 1ST KIND IS FOR GENERAL USE ABOVE APPROX 40 DEG F. TEMPERATURES.
the other type is an anti-freeze type for colder (snow/ice) climates.
(U don't want your reservoir to freeze, or it will burst, in 1 of these colder climates)
Other than that, u can use anything, even water (just don't use anything with ammonia, like Windex, or you'll smell thru the vents as u drive!