Cross Connection and Backflow Prevention

Backflow is an important issue that can pose a health hazard to your family. When backflow occurs, contaminants from nearby homes and businesses can directly enter your drinking water.

The good news is that there are simple and cost effective things you can do to protect your family from backflow contamination. The information below will help you accomplish this by explaining what backflow is and how it can be prevented.

Should you have questions related to backflow please do not hesitate to contact a MUB’ backflow engineer at 304-292-8443, email, or FAX us at 304-292-1526.

What is backflow and why does it occur?

Backflow is the unwanted flow of non-potable water and other substances in a reverse direction. This reverse flow of liquids, gases or substances can contaminate drinking water and pose a health hazard. Backflow occurs for one of two reasons—

  1. Backpressure: Backpressure happens when the pressure of a downstream (non-potable contaminant) source is higher than the supply pressure (public or consumers potable water system). Pumps, elevated tanks and boilers are likely to produce pressures higher than supply pressure and result in backflow.
  2. Backsiphonage: Backsiphonage is backflow caused by a zone of negative pressure (pressure less than atmospheric) in a water system. Atmospheric pressure pushing against a contaminant will force it into a potable water supply that contains a zone of negative pressure. The negative pressure is caused by a decrease in supply pressure due to such things as a water main break or fire hydrant use. The decrease in supply pressure causes a siphon effect (like sipping water through a straw) resulting in a reverse flow.

Naturally, for backflow to occur the potable water supply must be temporarily or permanently connected to a non-potable source. These connections are called cross connections and come in two basic varieties: Direct connections (i.e. piping) and indirect connections (submerged inlets).

A direct connection is created by connecting one pipe to another pipe or receptacle. The connection may or may not be valved. This type of connection is often installed where it is necessary to supply potable water to an auxiliary piping system (i.e., a hot water boiler, private well, or an irrigation system such as a lawn sprinkler system).

The other type of cross connection is a submerged inlet (or indirect connection). A submerged inlet is a potable water supply inlet that is below the flood level rim of a receptacle. The flood level rim is the edge of the vessel or receptacle from which water overflows. An example of this is submerging a garden house in pooling water or a sink in which the nozzle extends below the waterline of the basin.

Why backflow prevention is important

Water provided by MUB meets very strict criteria established by federal and state guidelines. This treated water is of extremely high quality and delivered to your home ready to use. The problem with backflow (whether accidental or intentional) is that it can introduce contaminants into drinking water without the knowledge of the user or MUB. Then, when used for bathing, swimming, cooking and drinking, this contaminated water can pose a health hazard to you and your family.

How to prevent backflow contamination

While backflow is a serious issue, the good news is that backflow contamination can be prevented!

Install Backflow Prevention Devices

MUB requires that customers with the highest contamination potential (normally nonresidential customers) take steps to protect against cross connections and prevent backflow to the water system. This protection includes the installation of an approved backflow prevention device as well as annual testing of the device by a certified tester. This practice follows guidelines as set under West Virginia Bureau for Public Health Legislative Rule 64CSR15 (See ‘Resources’ below).

Containment devices are required on a customer’s main domestic, fire, or irrigation line(s), as close to the water meter as possible, but before any branch off of the water piping occurs. MUB will determine if you will need a device to comply with the regulations and staff are available to answer questions related to backflow prevention.

MUB also encourages residential customers to take action to prevent backflow through the installation of prevention devices. While the cost of purchasing and installing any device is the responsibility of the customer, the safety benefits are well worth the investment. MUB does recommend that customers interested in installing such devices obtain cost estimates from as many service providers as possible before installation.

Take Action!

There are a number of everyday things you can do to prevent backflow. Here are some simple things you can do around your house:

  • Identify all cross connections within the home and remove them when possible;
  • Install backflow protection on all cross connections that cannot be removed;
  • Ensure that air gaps are maintained between water faucets and sink basin rims;
  • Ensure that hoses do not become submerged and are used in areas where they will not become submerged (i.e. filling a pool);
  • Ensure valves are turned off when not in use (simply turning off a properly functioning valve can prevent backflow);
  • Install hose bib vacuum breakers on fixtures (hose connections in the basement, laundry room, and on outside faucets/spigots). These are simple screw on devices that are available at any hardware store;
  • Install approved backflow prevention devices on lawn irrigation systems and on fire sprinkler systems;
  • Protect against thermal expansion by ensuring water hose valves are closed when not in use and install a thermal expansion device on hot water heating tank systems (for more on thermal expansion please see our FAQs and the Resources area provided below).

Don’t ‘just do it’! Keep them separated!

Avoid creating connections between auxiliary water systems (well, cistern, body of water) and the water supply plumbing. By avoiding cross connections you avoid sources of possible contamination for yourself and your neighbors. It should be noted that West Virginia legislative code mandates that “No person shall install or maintain an unprotected cross-connection in a public water system” (see §64-15-4. Cross-Connections of Legislative Rule 64CSR15 linked below).

Remember: MUB staff are here to help. Please do not hesitate to contact a customer service representative at 304-292-8443, email us at, or FAX us at 304-292-1526. We will work with you to answer any questions you may have regarding backflow prevention and the corrective actions necessary. Below are additional resources that may be helpful.