Originally Posted by ElevatorAssassin
Could this potentially harm the beer in any way? My batch is a bit short of five gallons (about 4 1/2), but I gather that if I add some water the gravity will fall to the target specified in the recipe and make it a bit lighter.
If you boil the water (and cool it) first, then probably you wouldn't have any harm. I guess I'd suggest tasting the beer first, and seeing how it is. If you want to water it down, then go ahead. I wouldn't, because then the beer might be "thin" and watery. I'd check the SG now and see if it's done. If it's not at FG, then wait until it is before deciding.