Actually, Antifreeze is exactly that... its purpose is to prevent the coolant from freezing, it also includes additives to inhib rust & sludge, as well as lubricating properties for your waterpump etc...
Pure H2O has a better capacity to absorb and dissipate heat, so your bike will actually run cooler on water than it will on antifreeze. Adding a surficant like Water Wetter to the water will improve it's heat dissipation ability, as well as adding lubricating and anti-rust properties.... However, your water will still freeze and break the waterpump impeller, at 32 degrees. -Sean