What goes wrong

Homes built after the mid-1990s usually have an ATC valve. In that case, simply sticking on a low-flow shower head to save water is a bad idea—the two technologies don’t work well together. That’s because most ATC shower valves are certified for the current standard flow rate of 2.5 gallons per minute (gpm), which has been a federal law since 1992.

Best remedy: Retrofit

While it’s expected that soon all new ATC shower valves will be certified to 2.0 gpm—and work better with today’s generation of low-flow shower heads—for now, the best way to retrofit an older shower is to get rid of your outdated faucet and install a new ATC valve and a new shower head. Buy them from the same manufacturer so you’ll know they’re designed to work together.

Checking for an ATC valve

How to know if you have an ATC shower valve? Most homes with single-faucet showers built after the 1990s have them. However, if your shower has a two-handle faucet, chances are it does not have one, no matter when it was built.

What do they cost?

You can buy an inline ATC shower valve that installs inside the plumbing wall for $200 to $400. These days, however, most faucet manufacturers include temperature control valves with their exterior water-control handles—they come as a single unit for $200 to $500.

Waterproof digital models with a programmable keypad install inside the shower and cost $400 to $700. Add $200 to $400 for installation.