The aerator on your faucet serves a very important function: by adding air bubbles, it helps to fuse the water and give it a softer feel. It also helps reduce the amount of water you use. So if you're faucet's water stream is acting funny (like a drop in pressure), it might be time to either clean or replace your aerator. If you're having trouble with your shower head, too, a little vinegar might do the trick.
This Lowe's video is brought to you by Delta, but these tips can be applied to any faucet or shower head. You'll need channel lock pliers, adjustable wrench, cloth, toothbrush, thread seal tape and maybe some white vinegar.