The only advantage of using water is it does not effect the a/f ratio as methanol does. The more methanol the more your guessing what a/f ratio to run. The timing has to be advanced and the a/f leaner like 12.5 :1 to make lots of power on h20. Sounds a bit scary, seems meth is more safer up to a point if you get the a/f dialed in ,but if you get carried away you will be in trouble just the same. Water doesn't burn it vaporizes to steam, add too much you'll slow down in a hurry.
Here is some info i found on it.
Research carried out during World War II indicated that pure water is best at suppressing detonation, while a 50/50 mixture of water and methanol permits the greatest power output before detonation occurs.
If water injection is used without any changes made to the tuning of the engine, improvements in power are possible but not probable. However, if the engine air/fuel ratio is leaned out, or boost is increased, or the ignition timing is advanced, more power is very likely. Supercharged aircraft engines using water injection had mechanisms that leaned out the air/fuel ratio simultaneously with the operation of the water injection. Testing on aircraft engines indicates that the mass of water required to suppress detonation is 20-30 per cent of the weight of the total liquid charge (that is, the water plus the fuel) being consumed. It is important to Distribute the water equally to each cylinder so some cylinders don't detontate before others.