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Backflow Preventer

What Is A Backflow Preventer And How Does It Work?

backflow preventer is a device that’s installed on your home’s water pipes that allows water to flow in one direction but never in the opposite direction. Its sole job is to prevent drinking water from being contaminated due to backflow.

But what is “backflow” and how does it happen? Is it something you need to be worried about as a San Francisco homeowner?

Don’t worry, we’ll answer all these questions and more. To start, let’s look at exactly how contamination can happen.

Have more back flow questions and need a San Francisco plumber? Just contact us.

How does “backflow” happen in the first place?

When water enters your home from the main water supply line, it should only ever flow in one direction: into your home.

But sometimes, due to pressure changes in the pipes, that water can actually flow backwards and seep back into the main water supply line. 

For example, backflow can happen when there’s a break in the main water line or when a fire hydrant is opened for use. Because pressure is lost during these events, water is no longer being pushed forward into your home and will flow backwards into the city water lines.

And when this happens, backflow can contaminate the public drinking supply with:

  • Fertilizers/pesticides

  • Human waste

  • Chlorine from pools/spas

  • Soap from sinks/dishwashers/showers

And that’s where a backflow prevention system comes in handy. Let’s take a closer look at how a backflow prevention system works.

A backflow prevention system… prevents backflow

Backflow prevention systems are devices installed onto a pipe that only allow water to flow in one direction

Think of it as a one-way gate that allows water from the city’s public water supply to flow into your home’s piping but stops water if and when it ever tries to flow backwards into the main water supply. 

For a better idea of how backflow preventers work, take a look at this diagram.

How do I know if I need a backflow prevention system installed at my house?

First off, any San Francisco County resident who has an irrigation system or a well is required to install a back flow preventer at the water meter (because both systems are at risk of contamination due to backflow).

Live elsewhere? Or are you a San Francisco resident without an irrigation system or well? If so, you’re probably wondering if you need a backflow prevention device installed at your home.

Well, we still recommend you have a backflow preventer installed anywhere incoming water and wastewater might be cross-connected

Newer homes may have built-in backflow preventers on certain water lines but in order to know for sure whether your home has proper backflow preventers set up, we suggest having a plumber inspect your home’s water system. They’ll install backflow preventers where it’s needed.