It depends. Sometimes, if you have an unchlorinated water source, it might not be needed. If your water company uses small amounts of chlorine, the aeration from the faucet may be enough to disipate it. If your company uses lots of chlorine (in summer, for instance, they often up the concentration) or uses any amount of chloramine (aeration will not disipate chloramine), it is absolutely needed. Better safe than sorry and it can't hurt. I use a basic dechlor that is for chlorine or chloramine (get one that does both just to be sure).