iPhone 4 dropped in water; now won't do anything

Dorothy, the first thing you want to do is to remove your battery. DO NOT try to power it up or anything else. Not sure when this happened, but if it was very recent, you can place it in a ziplock bag of dry rice etc. After that, you will have to disassemble your iPhone. Follow these Guides to get it done. After you have disassembled, clean it according to this guide. It was written for a 3G but all the points are still valid for your phone as well. After that, reassemble, replace the battery and re-evaluate. Hope this helps, good luck.