Why Water Is Coming Up Through Your Sink (and How to Fix It)

As annoying as a slow-draining sink or tub can be, it could be worse: Water—along with sediment or other gunk—could be coming up through your drain. Like our alimentary canal, our drains are supposed to be a one-way thoroughfare, and when they operate in reverse, things can get pretty unpleasant. That’s why I asked two veteran plumbers to explain what causes water to come up through our sink and tub drains, and what we should do if it happens.

Why is water coming out of my sink drain?

In order to understand why water is coming up through your drain, Roy Barnes, a plumber with roughly 30 years of experience, and the co-owner of Service Force Plumbing in Rockville, Maryland says it’s helpful to have an idea how a home’s plumbing works.

“The plumbing in your house is like a venous system: Small drain pipes connect with other drain pipes to feed into ever-larger pipes, which eventually lead to one big drain pipe—your mainline sewer pipe out to the street, or your septic system,” he says. “Homeowners can do a little problem-solving on their own with this information.”

For example, the bathroom sink drain flow into to the toilet drain before leaving the bathroom entirely, Barnes says. “So if only the bathroom sink is backed up, then the blockage is almost certainly just at the sink. And if the toilet is backed up but the sink is not, then the blockage is probably still within the toilet plumbing, rather than the drain pipe.” If both the sink and toilet are backing up, then the blockage is either in the pipe that drains the entire bathroom, or somewhere farther down the line.

“The big one is when there is a backup at the lowest point in the house,” says Barnes. “If you have a toilet or shower in the basement, or whatever the lowest drains in the house are, and those are backing up, it often means that the mainline is backed up, which is the biggest [plumbing] problem possible in the house. You can’t use any of the plumbing.” You’ll need to call a plumber right away.

What’s causing the problem?

So, what prompted your drain to work in reverse? When water flows up from a drain, it means you’re dealing with a clog or other type of stoppage further downstream within the system, says Mark Collins, a fifth-generation plumber, and the CEO of 1-800-Plumber + Air..

“It could be the result of improper things going down the drain like grease, which will lead to stoppages,” he explains. “It also could be a result of buildup within the pipes that hair and other bio matter can stick to, resulting in a clog.”

But it’s not always a clog: Water coming up through the drain could also be the sign of a much bigger problem with your plumbing system, Collins says, like a break in the line, roots growing in your sewer line, or a pipe that no longer flows downward because of the ground shifting or the growth of tree roots.

These aren’t problems to deal with yourself: You’ll need a licensed plumber to evaluate the system—potentially using a camera to do a visual inspection of the sewer line—and determine if further action is needed to resolve the issue.

What to do if water is coming out of your drain

No one wants to walk into their kitchen or bathroom and see their sink or tub drain working in reverse—especially since water coming up from the drain probably contains sediment, grime, and who knows what else.

Of course, you’ll want to stop the water as soon as possible to prevent further damage, but ultimately, Barnes says that it’s important to pinpoint the root cause of the issue. “The problem needs to be understood, not just as ‘how do we clear this drain,’ but ‘why is this drain backed up,’ because if there’s a grease problem, or a damaged pipe, or roots in the line, or LEGO or Hot Wheels down there, the problem will keep coming back,” he explains.

Don’t use water

As soon as you notice water coming up from a drain, Collins says you should immediately stop using sinks, tubs, showers—really, any kind of water—throughout your home to help prevent further damage. “All of your drain piping is connected, and using the water in one area of your home could lead to problems in another area.”

For instance, if you have a two-story home and the drain line for your entire house is clogged, and you turn on a sink on the second floor, it could cause the sinks and toilets downstairs to overflow, says Collins. “To avoid water damage to your home, I highly recommend you stop using water until the problem can be further diagnosed.”

Get rid of the water

Do your best to contain the water coming out of your drain until it stops rising. Then, if the water in the sink or tub doesn’t go back down the drain on its own, you may want to use a bucket to remove the water—especially if it smells bad.

Although Collins says it’s possible to dump the water in a sink or tub in a part of the home where the plumbing is working properly, he urges people to exercise caution, and only do this if you’re extremely confident that the problem isn’t affecting the other areas of the home. You might want to dump the gross water outside instead. Either way, Collins stresses that this is only a temporary solution, and you’ll still need to address the problem that caused the drain to back up in the first place.

Take the plunge(r)

According to Barnes, if a homeowner wants to attempt to deal with this problem on their own, they should stick to using a plunger. “The proper way to use a plunger is with a rapid in-and-out motion—not just push[ing] and wait[ing,” he says. “If a plunger doesn’t do the trick, most homeowners should be calling a plumber.”

Put down the chemicals

Both Barnes and Collins advise against using pouring chemicals down your drain in an attempt to get rid of a clog. “The illusion that [Drano and similar products] can clear any significant backup is just marketing, and in the meantime, you’re using a bunch of nasty chemicals,” says Barnes.

According to Collins, acid-based “drain opening” products aren’t just bad for your piping and plumbing fixtures, but they’re also dangerous for anyone working on them. “If the drain piping needs to be removed and they are filled with dangerous acids, it can be very dangerous for the plumber who is working on this within your home,” he notes.

When to call a plumber

Even if it appears as though you cleared the clog, Collins still recommends calling a plumber. “Drain problems don’t fix themselves—or, as I say often, a properly working drain line will never back up,” he says. “So, if you’re having drain issues it is always best to have a plumbing professional take a look at the system to make sure you do not have a bigger issue going on. Don’t ignore the early warning signs of slow flowing drains or gurgling sounds with your pipes.”