Cleaning under the hood

I live in chicago where they salt the roads heavily in the winter time. I try to wash my car at least once a week including the undercarriage in the wintertime to keep it from rusting and am wondering if i can use regular soap and water under the hood to get all the salt off of the body/frame around the engine. I don't really need anything such as a degreaser, as the engine isn't that dirty, im just looking to keep things from rusting under there. What kind of soap would be the best?