Some local breweries may have a water supply that they will allow you to purchase water from. I've been told that the Grain Belt brewery here in Minneapolis sells 5 gal jugs for pretty cheap. Something like $3.50 per jug. But to save the hassell you can just grab 5 gal of spring water from the local grocery store. Boil 2.5 gal for your wort and add the other 2.5 gal once you put the wort in the primary. No need to boil the other 2.5.