I have made a few batches of beer from those home brew kits sold at Brew n Grow. When I cook the beer, I only am boiling 2.5 gallons instead of the whole 5, per instructions, and then I add the other 2.5 gallons from my tap water. My question is, is they recommend a wort chiller. When I add the 2.5 gallons to get my total of 5 gallons, it naturally cools down the beer because the tap water is cold. What advantages does the wort chiller have? I suppose the tap water doesn't get it all the way cool, but does a great portion of the cooling, because basically it is direct cooling as opposed to heat transfer cooling through a copper tube. Does adding the 2.5 gallons of cold tap water introduce potential bacteria into my wort??
Any answers would be greatly appreciated!