What Causes Back Flow?

Backflow repair in Indianapolis, IN

Fresh, potable water is something that many Indianapolis, IN residents take for granted. In a developed nation, there’s never the expectation of having wastewater come flowing out of the tap. Unfortunately, this is an issue that can and does occur. Also known as backflow, it’s the sudden and unwanted reversal of water’s direction within a plumbing system. Backflow can send water that’s riddled with chemical and biological contaminants straight into your sinks, tubs, and shower pans. Worse still, there are times when you may not even know that it’s happening. In what follows, we’ll lay out several common causes of backflow along with tips for preventing it.

Back Pressure and Back Siphoning

Backflow prevention assemblies are a required part of all plumbing connections that have the potential to force contaminated water into either the municipal system or a private home or business. Unfortunately, these assemblies aren’t guaranteed to work all the time. There are two primary causes of backflow and they’re both related to pressure within your plumbing system and within the sewer system that it’s connected to. These are back pressure and back siphoning.

Back pressure occurs when pressure within the wastewater system exceeds that of the freshwater supply. One easy way to understand how back pressure works is by considering what happens when you raise an active water hose above the ground. Excess pressure within the hose creates a vacuum, and the fresh water that’s meant to flow out stays trapped within the hose. Back pressure often develops when a pump is being used to apply pressure to a plumbing system. However, it can additionally occur when water rises and becomes subject to gravity.

With back siphoning, heavy water use in other areas of the system or a break at the water main causes a dramatic decrease in water pressure throughout the main lines. This rapid depressurization creates a vacuum. Within seconds, this vacuum begins pulling water from other areas.

Residential wastewater removal systems are heavily reliant upon good ventilation and gravity. Imbalances in either of these areas can send fresh, potable water or contaminant-rich wastewater in the wrong direction. Excess pressure in freshwater or wastewater systems is always the cause of backflow. There are even times when wastewater systems have excess pressure and freshwater systems have insufficient pressure at the same time. When this occurs, gray water or black water will be forced into a home’s water supply lines.

Broken Backflow Preventers

Although backflows are the result of changes in system pressure, if you have a backflow occurring in your home, the most likely cause is a broken or missing backflow preventer. Having these valves in place for all at-risk connections is absolutely essential. Unfortunately, the likelihood of pressure fluctuations in wastewater systems and supply lines always exists.

There should be several types of backflow preventers protecting your freshwater supply. These include:

  • Pressure vacuum breakers
  • Reduced pressure zones
  • Double check valves

Although each has its own purpose and design, they all block the flow of water that’s moving in the wrong direction. In short, they prevent the two-way flow of water at all times and irrespective of pressure changes. As soon as water is released, backflow preventers close connections off so that water cannot reverse direction and flow back in. Like all components that are constantly subjected to moisture and water pressure, backflow preventers can eventually become corroded. When backflow valves rust and develop other corrosion-related wear, they must be replaced entirely.

Many backflow preventers have rubber components. Changes in water temperature, exposure to high pressure, and constant moisture can cause these components to dry out, crack, and shift. Given that they’re designed to provide watertight seals, any changes in their integrity can allow nominal amounts of water in. Issues with damaged rubber seals are especially dangerous to building residents. Having even a very small amount of wastewater enter a home’s freshwater supply lines can result in illness. A single drop of wastewater can carry a number of potentially deadly contaminants.

Aging backflow preventers that are severely degraded can be fully or partially forced out of place by any sudden and significant change in water pressure. Whether subjected to back siphoning or back pressure, these units might not be strong enough to stand up to the forces at play.

At a minimum, backflow preventers should be installed at all automatic refill lines for swimming pools and other outdoor water features. Landscape irrigation systems should have backflow preventers as well. Garden hoses and other exterior faucets should have hose bibb breakers. All backflow preventers used in residential applications should be in-line testable. This means that it must be possible to test them during times of active water service. Without these preventative installations, contaminated water could flow into the home whenever downstream pressure exceeds upstream pressure, or other pressure changes occur.

Signs of Backflow

When backflow preventers are severely damaged or missing entirely, there will often be telltale signs of wastewater infiltration. Your tap water might have an eggy, sulfurous smell or a yellowish tinge. Cloudy water or water that both tastes bad and has an unpleasant odor are all causes for concern. If you notice any of these signs at any tap in your home, call in our plumbing professionals from Cooper’s Water. We can perform backflow testing to verify whether or not your fresh water is contaminated. We can also identify the exact backflow preventer that’s missing or malfunctioning.

It’s important to note that it isn’t just your home’s backflow preventers that can affect the purity and overall safety of your home’s water supply. If your neighbor has a damaged backflow preventer, wastewater from their home could be entering yours and bringing soap, fertilizers, and other chemical or biological contaminants along with it.

Slow-Draining Showers, Tubs, and Sinks

Even when they aren’t corroded or excessively worn, backflow preventers can still cause problems. They may be clogged or covered in debris. This is likely the case if you have a blocked or slow-moving drain in your home along with foul-smelling water. If cleaning out the drain cover or drain catch doesn’t resolve the issue, reach out to our licensed plumbers. This is one of the top reasons why homeowners are advised against using store-bought drain cleaning solutions, plungers, and drain snakes. None of these tools will resolve the drain issue if the problem lies at a nearby backflow preventer.

Changes in Water Pressure

Buildups and blockages at backflow preventers can also cause changes in your home’s water pressure. If your shower spray suddenly isn’t strong enough or if your washing machine is taking a lot longer to fill, a small rock might have gotten snagged in the backflow preventer, and it could be keeping this unit from fully opening or fully closing. Fluctuating water pressure can also be the result of defects in preventers. If you have excessively hard water, highly acidic water, or low-quality water in your area, these safeguards may need to be replaced more often than normal. Depending upon their type and location, most backflow preventers will last up to 10 years. Water quality issues and other environmental concerns may make it necessary to have them swapped out more often.

Since 1980, Cooper’s Water has been proudly serving residents of Indianapolis, IN with a complete line of plumbing services. We offer water filtration, water softening, and drain cleaning services. We also provide hose bibbs, backflow preventers, and backflow inspections. Get in touch with us today to schedule an appointment!


Cooper’s Water has been providing water softener services in the local area for more than 40 years. As the recipient of the Angi 2020 Super Service Award and a Best of HomeAdvisor 2020 Winner, we have built a reputation for excellent customer service. All our water softeners come with a seven-year quality guarantee and we provide free estimates as standard. If you are looking for a high-quality, water softener for your home, please contact Cooper’s Water today.

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