Water to fluid ratio is quite straight forward to calculate
But if you want specifically on the cooling effect due to evaporation, you need to take the latent heat of each liquid into account and re-calculate to that effect.
Some time ago I have made a chart up to show how much water is require to replace the rich-air/fuel ratio, here it is again - It was done quite quickly and do point out any mistakes plaese:
This one I have included 25% of merthanol:
