Air filter cleaning?

Hello. I was recntly reading through K & N's directions on cleaning an air filter. They made several mentions of K & N cleaner and K & N oil. I'm wondering if they are just trying to sell more product and can the filter be cleaned with just water. Also, how important is the oiling of the filter?

If you want to keep using it get their recharge kit - just don't over oil it. Can't clean it with just water. Have the same one in my car since '01. If it's really dirty and don't want to buy the kit you can always toss it and get a stock paper filter...up to you.