Download this document so that you can calculate your personal water footprint. You need to save it as an Excel document. Then open it and fill it in.
You can also try this online water footprint calculator (up till indoor water). Results are in gallons, though. Ever heard of gallons?
1 US gallon = 3.78541178 liters
This is another calculator you might want to try, especially if you want to find out more about virtual water.