An aerator is a simple device that mixes air with water from your faucet. The air cuts the flow so you use less water. It also keeps the water from splashing so much in the sink. You can buy aerators at most hardware or plumbing supply stores for a few dollars, but first check your faucet to be sure it has a screw thread on either the inside or outside of its mouth. If it doesn’t, there’s a device called a “universal faucet adapter” that you’ll need.