I have always been an extract brewer, and always topped my primary with tap water (~2 gal), with no detrimental effects. My water is chlorinated, but I don't taste it. I read all the time that you need to boil any water added to the brew process. Is this needed? I have never read of anyone who has had a detrimental effect due to their water. Is everyone boiling their water? Do we need to? I'm just curious.