iPhone 4 falling in water - issues after fixing
Yes, it is possible, even likely, that one or more of these issues was caused by immersing the iPhone in water. You should seek repair quotes from Apple or other repair sources, but you'll most likely find that replacing the phone is the most economical solution. Check Craigslist and similar places for people selling their iPhone 4's after upgrading to a 4s. 

If you're of a DIY mindset, iFixit provides repair information, parts and tools for fixing portable electronics.