Pain with 3rd party authorised mac repairmen

[o2xygen]

So anywho, I recently had an issue with my macbook unibody. The power adapter would not charge so I contacted applecare and they recommended that I take it into a 3rd party store, and tell them to test a new power adapter, because that was what he thought was wrong.
So I took it in, they held it for 4 days, before telling me that my one month old macbook had water damage which is not true, I take very good care of my mac's. My warranty is now voided and I have to fork out $200 to get something inside replaced.

Im slightly curious to find out whether or not I have any rights at all over this, because arguing with them over the apparent water damage wont get me anywhere. Im also curious, if I get this water damaged part replaced, will this put me back under warranty again, seeing there wont be any evidence of water damage?