Running straight water is extremely bad. For one rust in your block. Second if its running straight water what happens is the metal surfaces that the water "trys" to cool is so hott that the water doesnt actually take heat away from it because little air bubbles form on the metal surface. So the water never gets a chance to cool off the metal surface. Ill post a link that better describes it than my jargon. Coolant basically helps cool the block more than straight water. You will most likely overheat.
Watch this little video
http://www.redlineoil.com/products_c...coolantFlash=1
BTW nice to see another wisconsin boy.