I am thinking about buying a 21.5 imac for sketchup design work. I would love to know for sure that I can upgrade the RAM...

You can try leaving it in a zip lock bag with a bunch of rice for a week. The rice is supposed to absorb the water. Maybe also leaving it in the sun. Sometime electronics can recover from water damage as long as you don't try to turn them on before they are completely dry. It could still be okay if you tried to turn it on already, but there is also a chance that the water conducted electricity to a place it shouldn't have thereby shorting a circuit. Sorry I don't have a better answer, maybe someone else has a more thourough understanding of what you should do. I hope your data is backed up.