On pretty much any house a home inspector inspects, the inspector is likely to call out a cross connection. A cross-connection, simply put, is a condition where contaminated or non-potable water can come into contact with the potable water supply in the home. Common issues include:
- Lack of a dishwasher high loop
- Missing hose bibb anti-siphon devices
- Missing backflow preventer on irrigation or pool auto fill
- Lack of an air gap between the faucet and a sink/tub
Why are these an issue?
If there is a decrease in the pressure in the supply line going to the house, this can create back pressure or back siphonage, which can draw the non-potable water back into the house’s water supply. Common situations that can cause this backflow are a break in a public water supply line or perhaps firefighters using a public supply to fight a fire. If the pool’s auto-fill backflow preventer is missing and a decrease in pressure occurs, this could draw the stagnant water from the auto-fill basin back into the home’s water pipes, which can cause health problems.
With the case of the dishwasher’s high loop, wastewater from the garbage disposal or kitchen sink can make its way back into your dishwasher contaminating your clean dishes. The dishwasher drain line should be secured several inches above the connection to the garbage disposal or waste line with a clamp.
The most common devices use to prevent backflow are an atmospheric vacuum breaker or a double check valve for irrigation and pool auto-fills and an anti-siphon device for a hose bibb. These are shown here:
Hose Bibb Anti-Siphon Device Atmospheric Vacuum Breaker Double Check Valve