These days most watercooling devices are very safe. Back in the day of home-made versions, you needed to be a little more careful.
Are you planning on doing some serious overclocking? If not, then I would not waste time or money on watercooling. There are perfectly good Heatsink and fan units on the market that will suffice for where a overclocking etc is concerned.
Example watercooling kit:
http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=375007
If you go watercolling, study up. It may be your best bet to buy a kit rather than assemble the unit yourself from the various accessories you'll need to buy, however, you'll gain a better understanding of your rig.