Can Low-Flow Showerheads “Explode” and Flood Your Older Home?
The short answer is yes. Older plumbing joints may not be ready to handle the sudden force released when water efficient new shower heads restrict the flow. Here’s how to avoid such surprises.
It happened to me. In my ever-vigilant effort to squeeze energy and water efficiency from my 100-year-old home, I installed a 1.8 gallon per minute shower head to replace the 2.5 gpm model of yesteryear. I had installed even lower flow rates (down to .5 gpm) in other buildings in the past, with no leak problems. But this time, it was clear that my existing copper plumbing was having none of it.
First, water started pouring down from the ceiling in my kitchen. This happened just after my wife finished a 10-minute shower. My immediate thought was that the drain must have come disconnected inside the ceiling joists, so I tore out a few of the ceiling tiles installed by the previous owner. To my relief, the old copper soldered drain was intact. Replacing it would have meant tearing out the tub, in all likelihood. What else could it be?
I went upstairs and turned on the bath, ran it for a while. No leaks. I filled the tub all the way to the top of the overflow drain. Still no leak problems.
Then I pulled the shower diverter valve. As you see from the photo, water began pouring out of both hot and cold water handles. It also began flooding the kitchen ceiling (again). I had a theory. I popped off the new showerhead and pulled the valve again: This stopped the leak from the ceiling and the backflow from the handles.
Pressure Vs. the Weakest Link
I knew that one of the most common leak spots in a tub spout is the short pipe that extends into the mixing valve, typically ½-inch soldered copper, or a rear-threaded piece of brass or plastic (if you’re lucky).
In old tubs, these are more often soldered into the mixing assembly behind the wall, meaning that if you break the bond, you could have a major plumbing repair on your hands, requiring you to tear into your shower wall. My spout nipple had rear threads, and I noticed it was a little loose. I unscrewed it fully, added Teflon thread sealant, and screwed it back in. Here’s a lot more detail, if you need it.
When I ran the shower again, I had solved the flooding of the kitchen ceiling, but water still poured from the handles. So I had “fixed” the immediate leak but not addressed the potential problem of a pressure mismatch in my plumbing. The restrictive nature of the showerhead was causing water to backflow all the way into my shower handles.
Plumbing Problems: The Hammer Effect
Plumbing is plumbing, right? If the pipes are sound, the pressure of a typical home shouldn’t cause a leak when your low-flow shower turns on. That’s why this is generally an old house problem.
A typical tub spout, with no special flow restriction, can blast water at up to 8 gallons per minute, at about 60 psi. You want that high speed when you have a set goal in mind—drawing a bath. Now shut that flow off suddenly, as the system shoves that water through a 1.8 gpm pipeline. It’s like hitting those pipes from the inside with a hammer. You’ve cut your flow down to less than one fourth in an instant.
Another little known fact is that city water pressures can vary dramatically. For example, pressure on top of a hill might be 40 psi lower than pressure at the bottom of said hill. I read that some City pressures run as high as 140 psi. Do you really want to test that much pressure inside 50- or 100-year old pipes with soldered joints? Add in the low-flow hammer effect and you may pass your pipe’s integrity threshold. Fortunately, there are some things you can do to address these issues.
You have a couple of ways to retroactively plan for your new low-flow shower head. First, you can install a pressure regulator. The better ones are adjustable. For example, this one lists for under $30 on Amazon (shown below), and allows you to set your pressure where you want it. This can also be helpful when installing water filters, which are designed with a specific range of water pressure in mind.
Another approach is to install an expansion tank, although this is more of a resilience measure than an immediate fix. What it will do is keep your hot water pipes from becoming overpressurized as hot water expands and then cools and contracts. Your low-flow shower plumbing will take an extra jolt if turned on when the pressure is high.
You’ll notice I haven’t suggested getting rid of your low-flow showerheads. Switching to this technology is essential for water conservation. In my opinion, even if you have to open up your old shower wall and replace the shower pipes with new, pressure-hardy PEX or CPVC, the expense is worth the lifetime water savings of frugal water flow.
Leak Sensors: The Last Defense
Finally, what if you already have a low-flow shower, but you’re concerned about your home’s plumbing reliability? It’s not an idle concern. I know several people personally who have had their home virtually destroyed by plumbing leaks. One of them is still in negotiations with the insurance company, so I can’t share his name. Another is my brother, who has had to replace an entire basement apartment due to the leaking bathroom on the first floor.
One “peace of mind” option is to install one of the smart leak detection devices that shut off your household water instantly if a leak is detected. For example the Phyn Plus system has this capability.
Another less robust but budget option is to install some WiFi enabled leak detectors. I’ve used products such as Govee sensors that send a signal to my smartphone if they detect a leak. This may not save your home from damage completely, but it could reduce the overall flooding.