1. Install low-flow fixtures. Most low-flow showerheads and faucets aerate water, which means you use less energy heating it. There is often no need to replace an entire sink — the important part is the aerator (the screw-on tip of the faucet), which determines maximum flow. This simple, cheap part could save you a bundle on hot water costs. See the hot water info page on the U.S. Department of Energy (DOE) site for more on this topic.