What Is a Cross Connection in Plumbing?

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    A cross connection is a point in a plumbing system where a potable water supply can potentially contact a non-potable one. This leads to a degradation of the quality of drinking water in your home or business. 

    Examples of cross connections include:

    • A piped connection supplying potable water to an industrial process, such as a cooling tower
    • A garden hose lying in a cesspool or submerged in a pesticide mixture
    • A submerged irrigation system outlet
    • Connections to firefighting tools halting water supply to buildings

    Read on to learn the answers to questions such as What is a cross connection in plumbing, why it occurs, and whether you can stop it. 

    How Does a Cross Connection Occur?

    A cross connection in plumbing occurs when there’s backpressure or back siphonage. In both of these processes, either positive or negative pressure occurs, forcing the water to flow in the reverse direction, commonly referred to as backflow.

    What is Backflow?

    Backflow refers to the unwanted backward flow of nonportable or used water from an industrial, domestic, or institutional water distribution system to a portable water supply system.

    It occurs when the system pressure does not balance correctly with the supply pressure. When this happens, and a cross connection is present in the plumbing system, it can contaminate potable drinking water.

    Backflow occurs as a result of:

    1. Back Siphonage

    Black siphonage refers to backflow due to negative pressure in the water system piping. 

    The pressure creates a vacuum or partial vacuum, forcing water to flow in the reverse direction. This process is pretty similar to what happens when you sip a drink through a straw. 

    When the water distribution system pressure falls below atmospheric pressure, the reverse of what is intended happens-backflow. 

    For example, if the water supply halts due to fire fighting leaks or repairs.

    2. Back Pressure

    Backpressure is the reversal of normal flow in a system due to positive pressure. That means that the pressure in your plumbing system is higher than the pressure in the supply piping.

    Often, this happens in installations such as elevated tanks, booster pumps, heating systems, and systems that produce high pressure.

    Is Cross Connection Dangerous?

    Waste water contaminating your drinking water is a critical situation. And what’s worse is that it doesn’t only happen to you but may affect other homes connected to the same supply pipe.

    When the cross connection happens, the non-potable water may reverse back to the clean water via the faucet, especially if there’s no draining in the supply piping. In some severe cases it can even flow backwards into the public water system and cause a serious contamination in the potable water system.

    Can You Stop Cross Connection?

    Backflow preventers are essential in curbing the problem of cross connection. Similarly, by installing hose bib vacuum breakers on hose spigots, you prevent the situation. 

    Besides installing a backflow prevention device at home, avoid submerging hoses in swimming pools or places such as tubs and sinks. This also helps with backflow prevention.

    Air gaps are also an effective way of preventing backflow. These are open vertical spaces between spots where wastewater can collect in any equipment or device linking to your plumbing system.

    Cross Connection Inspection

    A cross connection specialist is a professional tasked with conducting cross connection inspections to ensure no cross connections in a home or business’s plumbing system.

    If your building connects to a municipal water supply line, it’s recommended to have a cross connection inspection done every once in a while so the water service does not suffer any interruptions.

    Related Posts
    What is a backflow preventer
    Anti siphon valves vs backflow preventers

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