Throughout the United States there have been numerous documented cases of potable water systems being contaminated as a result of unprotected cross connections. In many instances these cross connections and backflow situations resulted in illness and in some cases death. Cross connection control and backflow prevention measures are established in national and most state and local regulations. They should be continually enforced.
The definition of a cross connection is a connection between the potable water system and a non-potable substance, which can be a gas, liquid, vapor or any other substance not part of the potable water supply. This interconnection becomes a potable water system hazard when a backflow condition is introduced by any number of causes such as a water main break, fire, pumps actuating, elevation changes or high demand. Whatever the type of cross connection, it's important to remember that potable water contamination can go undetected due to dilution.
One example of a cross connection and backflow situation occurred at a large facility having an irrigation system on-site that was supplied by both a pond and the city water supply. The cross connection was discovered after the water company received a call from an employee of the facility on a Monday morning who complained that people were getting sick after drinking the water. Later that day and upon investigating the problem, the water company discovered two interesting facts. There was a zero chlorine residual in the office building and the 5 acre pond next to the building had gone dry over the weekend.
It was later determined by the investigation team that the potable water system had been interconnected with the irrigation system being supplied by pond water. The potable water system had a double check valve assembly backflow preventer installed at the connection point to the irrigation system. The backflow preventer was the wrong type and had not been tested since it had been installed (approximately three years). Test results showed both check valves in the backflow preventer were fouled and leaking. As a result, the water in the pond had been pumped into the irrigation system at 90 psi, while the city water pressure was 70. City meter readings revealed the meter had ran backwards close to one million gallons. All that water in the pond had not only been pumped into the office building, but into the city's potable water distribution system.
There are many types of water using equipment and processes that can create cross connection hazards as described above. Cross connection control and backflow prevention is a continuous effort and must be diligently pursued. Private facilities must also protect the water by ensuring cross connections are protected as established by these regulations.