How much water/meth to the fuel is best?

[lowride]

I have made a simple water "humidifier" in my stock VW TDI, and get mileage gains with 3-5% water to the fuel. I have tried with 20% up to 100% water without problems short term. But I wonder how much water/methanol you guys are injecting, in % to the fuel?
A Suede in Norway

[Richard L]

In most application we recommend beten 10-15% of water to feul. We have tried 600% water to fuel (diesel engine), the engine still ran but not very happy. Plenty of unburnt fuel came out of the exhaist pipe.