You need to do what Ben suggests and you need to clean all the internal components gently/carefully to remove anything the water has left behind (dirt/soap/calcium/copper, etc.) If you just dry the phone it may short/rust out later on. You can use distilled water/high % alcohol solution and soft brush. Use any guide for an iPhone 4, by the looks of things the concept is the same? Electronics Water Damage, this a 3G but it shows the residue/damage likely if you don't clean. Repairing iPhone Liquid Damage

I'd also suggest getting a new battery. They just don't tend to like water and once you have a known working power source then troubleshooting will be easier. Good luck and let us know how you get on .