Water itself doesn't have an octane rating at all... don't see where anyone said that it did.
It is an octane booster for the fuel when it is injected with the fuel during combustion.
Its too bad water and fuel dont equaly mix we could just put water right in the tank to boost the octane, vice having to spray it in seperately lol
My take on it... if your already intercooled and dont have an iat problem and dont need to supplement your fuel system theres really no need for meth part of it at all, you could use 100% water to boost octane, cool the cylinder and increase timing if you like. Or if you do use a mix the 20-30 percent mix in the cheapo wiper fluid is fine to cool the air a littel more as well. The meth becomes important when you trying to cool iat's without an intercooler of some sort, that when you want a higher concentration of meth ie 50% or more.