if you're using an LCD display, yes water is okay; they also make LCD cleaning solutions which probably do a better job... for CRT, you can generally use windex sprayed on the towel, not the screen (if it drips down the screen, it could go behind the plastic... 🙁)
if you can, i'd go to compusa or bestbuy or somewhere and buy some screen cleaner for whatever monitor you have... the LCD cleaner conditions the plastic i think, and the CRT cleaner is designed not to corrode the anti-glare coating.
pnw