Does pre- matter?

I translated a word that would be "pre-wash" in English. As I was typing it out, I wondered if the spelling should be "pre-wash" or "prewash" (one word). When I was learning spelling, usually the prefixes were supposed to be followed by a hyphen. However, it seems like they don't have to be anymore. But I don't know if I want to make it one word because the concept of "before" is emphasized by the hyphen--it's a PRE-wash, not POST-wash (though there really is no such word).