I use half a campden tablet to treat 10 gallons of water, stir it up well and let it sit while I set up everything else for brew day then I start heating my strike water. That takes care of the chlorine for a 5 gallon all grain batch.
I have found chloramine levels in my water to be highly variable. When there is a new subdivision coming online nearby, or a heavy rain causes turbidity in the lake (our water source is a small man-made lake), they add more chloramine to the water to kill off the extra pathogens; before I started treating everything I had batches that were perfect, while others were almost undrinkable with band-aid flavor. Campden tablets are cheap insurance, and they are easy to use, so I would recommend always using them to treat any water which contacts wort or grain.