What is cross connection?
A cross connection is a point in a plumbing system where the potable (pure, drinking water coming into the house) is connected to a non-potable source. A cross connection exists when the drinking water system is or could be connected to any non-potable source such as a plumbing fixture. Pollutants can enter the water system through uncontrolled cross connections when backflow occurs.

There are two types of backflow:
  • Backflow can occur due to siphoning if the pressure in the water supply suddenly drops to a low level. This can happen if the municipal water pumping system fails, a municipal water line breaks or when fire trucks pump from fire hydrants. In each of these cases, the pressure in the water supply lines may drop below atmospheric pressure as the lines drain, creating a vacuum which can pull water (and any pollutants or contaminants) from a garden hose and into the water supply lines.
  • Backflow can occur due to back pressure if the pressure in a garden hose exceeds that in the supply pipeline. This can occur if pumps such as chemical injectors are connected to the garden hose. However, when injection pumps are used to inject chemicals into hoses or pipelines that are directly connected to municipal water supplies, hose connection vacuum breakers do not provide adequate protection of the water supply. Reduced pressure principle backflow prevention devices are the only acceptable backflow prevention devices when chemicals are injected into hoses or pipelines that are connected to municipal water supplies.

Backflow due to back pressure can occur even when pumps are not used. For example, if a spray nozzle which can be shut off with a valve is used on the end of the garden hose, and that valve is closed but the faucet is left open, the pressure in the hose will equilibrate with the water supply pressure, and the hose will expand in response to the supply pressure. However, a sudden large water usage in the house or at another location can cause the supply pressure to drop. This will cause the hose to contract, forcing water from the hose back into the municipal supply.

Pressure can also build up in a pressurized hose if air is trapped in the hose and then expands as it heats in the sun. This pressure buildup can force water from the hose backwards into the water supply pipelines. Hose connection vacuum breakers will prevent backflow from occurring from these sources by opening to relieve the pressure build-up as soon as the pressure in the hose becomes greater than the supply pressure. (UF/IFAS Hose Connection Vacuum Breakers for Backflow Protection (PDF).

Show All Answers

1. If water is under pressure how can I have backflow?
2. My outside faucets are new and have vacuum breakers built in, are there other things I need to be concerned about in back flow protection?
3. What is cross connection?
4. Why is the City doing this program now?
5. Is this an ongoing program?