Like majorvices, I use an in-line carbon filter for all my brewing water. Easy.
I see people using 10" x 2.5" carbon blocks fed by a garden hose, and it makes me cringe.
A 10" x 2.5" carbon block typically has a max flow of 1 gpm, so we typically recommend people go with half of that, or 0.5 gpm.
Garden hose flow is typically about 5 gpm - 10x the desired. When you push water through the carbon faster than it can be treated, you'll have chlorine in the treated water.
I rarely see mention of flow rates through carbon in the brewing forums.