If you've spotted a watts 900 backflow preventer in your utility room or basement, you're looking at a classic piece of plumbing history that's still doing heavy lifting today. These devices are essentially the bouncers of your plumbing system; they make sure water only flows in one direction and kick out anything that tries to sneak back into the main supply. While Watts has since released newer models, the 900 series remains a common sight in many older homes and commercial buildings because, frankly, they were built like tanks.
What's the deal with the 900 series?
The Watts 900 is what we call a Reduced Pressure Zone (RPZ) assembly. Now, that sounds a bit technical, but it's actually a pretty clever setup. It's designed to protect against both backpressure and backsiphonage. Think of it as a double-layered safety net. It has two independent check valves with a relief valve sitting right between them. If the pressure drops on the supply side or spikes on the downstream side, that relief valve opens up and dumps the "bad" water out of the system before it can contaminate the clean water line.
One thing you'll notice about the watts 900 backflow preventer is its weight. These things are usually made of heavy-duty bronze. Back when they were the standard, the goal was durability. You won't find much plastic on these old-school units. They come in sizes ranging from small 1/2-inch versions for residential setups all the way up to 2-inch monsters for bigger jobs. If you have one, it's probably been there for a couple of decades, which says a lot about how well they were made.
Why is my Watts 900 leaking?
This is probably the number one reason people start Googling their backflow preventer. You walk into the garage or the mechanical room and find a puddle under the device. It's frustrating, sure, but it doesn't always mean the whole thing is shot. In fact, a watts 900 backflow preventer is actually designed to leak when something is wrong—that's the "relief" part of the relief valve.
Most of the time, the leaking (or "spitting," as plumbers call it) happens because a little bit of grit or sediment got caught in one of the check valves. Even a tiny grain of sand can prevent the rubber disc inside from sealing perfectly. When that happens, the device senses a pressure imbalance and starts dumping water out of the relief vent. It's doing exactly what it was designed to do: protecting your water.
Another common culprit for leaks is simply old age. The rubber parts—the diaphragms and O-rings—don't last forever. Over ten or fifteen years, they can get brittle or lose their shape. If your 900 starts constantly dripping, it's usually a sign that it's time for a rebuild kit rather than a total replacement.
The difference between the 900 and the 009
If you start looking for parts, you might get a little confused between the watts 900 backflow preventer and its younger sibling, the 009. They look similar and do the same job, but they aren't the same. The 900 is the older, "large-body" design. It's significantly bigger and heavier than the 009.
Around the late 80s and early 90s, Watts shifted their focus to the 009 series because it was more compact and easier to install in tight spaces. However, many technicians still prefer the old 900 because the internal parts are a bit more robust. Just make sure when you're ordering a repair kit, you're looking at the right model number. Putting 009 parts into a 900 body is a recipe for a very wet afternoon and a lot of swearing.
Maintenance and the yearly test
You might be surprised to learn that in many places, you're actually required by law to have your backflow preventer tested every year. It's not just a way for the city to nag you; it's a public health thing. If everyone's backflow preventer failed at the same time during a water main break, the entire city's drinking water could get contaminated with whatever is sitting in people's sprinkler systems or boiler lines.
Testing a watts 900 backflow preventer involves using a special gauge to measure the pressure across those internal check valves. A certified tester will hook up hoses to the tiny "test cocks" (the small valves on the side of the unit) to make sure everything is opening and closing at the right pressures. If it fails the test, it usually just needs a good cleaning or a new set of rubber seals.
Can you fix it yourself?
If you're handy with a wrench, you can definitely handle the basic maintenance on a watts 900 backflow preventer. Taking it apart isn't overly complicated, but there's one huge warning: Watch out for the springs.
The springs inside these devices are under a significant amount of tension. If you just unscrew the bolts on the cover without being careful, that cover can fly off with enough force to do some real damage. Most pros use a C-clamp or a specialized tool to hold the tension while they loosen the bolts. Once you've got it open, you'll see the check assemblies and the relief valve stem. Usually, you just need to wipe everything down, check for cracks in the rubber, and maybe apply a little food-grade silicone grease to the O-rings.
But—and this is a big "but"—even if you fix it yourself, you still need a pro to come out and certify it if your local water authority requires an annual test. You can do the mechanical work, but you can't sign off on the legal paperwork unless you've got the certification.
When is it time to let go?
As much as we love these old bronze units, there comes a point where a watts 900 backflow preventer just isn't worth fixing anymore. If the internal brass seats are pitted or corroded, even a brand-new repair kit won't stop the leaking. At that point, the metal itself has worn down to where it can't form a seal.
Also, if you find that the cost of a full rebuild kit and the labor to install it is getting close to the price of a brand-new 009 unit, it might be time to upgrade. The newer models are often easier to find parts for at your local hardware store, whereas 900 series parts sometimes have to be special-ordered from a dedicated plumbing supply house.
Final thoughts on the Watts 900
At the end of the day, the watts 900 backflow preventer is a bit like an old truck. It's heavy, it's built out of solid materials, and it does its job without any flashy bells and whistles. It's a crucial part of your home's safety system that usually sits in the dark and gets ignored until it starts making noise.
If you take care of it, keep the sediment out of it, and replace the rubber bits every decade or so, it'll probably outlast most of the other plumbing fixtures in your house. It's one of those rare examples of "they don't make 'em like they used to," and for many homeowners and building managers, that's exactly why they keep them running. Just remember to respect the spring tension, keep an eye out for "spitting," and make sure you get it tested once a year to keep the water department happy.