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Why Do Storm Drains Steam?

Normally you probably don’t give storm drains much thought. Unless there’s a big storm happening, they’re usually an invisible part of your yard or the city you live in. Sometimes, though, you might see steam escaping from a storm drain. Why do storm drains steam? Let’s explore.

Sewers are Warm

Most things that we flush down our sewers come from within our homes. That could be water from a shower or washing machine, water from washing dishes, or you know, the contents of our toilets!
In any case, these are generally hot liquids. As they travel through the sewers under storm drains, those hot liquids come into contact with the air. If the air is cold, that can result in the formation of steam. It’s the same reason you can see your breath when you breathe on a cold day.
That steam can escape, traveling up through the drain system and escaping from a manhole cover. If you see storm drains or sewers steaming on a hot day, that’s usually the cause.

Steam Is Used to Heat Cities

In some cities, steam is actually used for heat. For example, New York City has over 100 miles of steam pipes, which are used to deliver heat for buildings. 
The steam is about 450 degrees. It’s actually one of the greenest energy choices for heat around.
If you see steam coming from the sewer or a storm drain in a city, especially if it’s coming from a big orange smokestack installed in the street, it’s probably from a leak in the city’s steam heating system.

Leaks and Electrical Equipment

Even if your city doesn’t have a steam heating system, leaks could still be the culprit. If water leaks from an underground pipe and then comes into contact with hot equipment or a hot water pipe, it can also turn into steam and escape from a storm drain.
Especially in older cities, this kind of steam is fairly common to see in the winter.

Do You Need to Do Anything If You See A Storm Drain Steaming?

If you see steam coming from a storm drain, it’s usually not an emergency. Especially if there’s a smokestack or cones in place, the local utility may already be aware of the issue. 
To be sure, though, you can often call your city’s utility to check in about steam leaks. Detroit for example has a special number for doing this, and your city may too. 

The exception is if you’re seeing smoke rather than steam. If that’s the case, you may notice a darker color and an acrid smell. If you notice smoke coming from a storm drain or manhole cover, dial 911 or call your local emergency services and report it because it could be a fire underground.

Usually, though, steam from a storm drain is not big issue. It’s just part of city life. You could think of it as kind of beautiful. Some movies even have fake steaming storm drains to create that city feel!

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