Mesa customers may not be aware of the extent to which Mesa expends its efforts to protect the water from the possibility of contamination while it flows through the distribution system. Water may be contaminated when a water supply line is connected to customers' equipment containing a non-potable substance such as a tank filled with acid, or a hose that drops into a bucket of cleaning solution. These cross-connections, permanent or temporary, would be dangerous if no protective measures were taken.

Water distribution systems are designed so that water flows in a certain direction from the distribution system to the customer. However, hydraulic conditions within the system may deviate from the "normal" conditions, causing the water to flow in the opposite direction. This "backflow" occurs when the pressure in the distribution system drops, siphoning water from the customer's pipes into the distribution system. This type of backflow is called back-siphonage and may occur when there is an unusually high use of water or undersized piping in an area. During fire fighting, or when a main water line breaks, water is siphoned to the point of high usage, possibly drawing non-potable substances with it and filling the water line with these substances. Some water customers have non-potable materials on their premises that are under pressure. When an unprotected water line is attached to the container or pipes holding the pressurized material, the material may be "pumped' back into the potable water system. This type of backflow is called backpressure.

Mesa protects the water from the possibility of contamination with backflow prevention devices.

Because of these potential dangers to the customer it is necessary to control cross-connections. There are several types of mechanical assemblies that serve as backflow preventers and are designed to work under backsiphonage or backpressure conditions. Mesa staff works with the Orange County Health Department and the California Department of Health, as well as area agencies to assist customers with procedures for installing and maintaining backflow prevention devices to comply with laws protecting the public water supply.

For questions about backflow prevention, contact Piet Pijl, Mesa's Cross-Connection Specialist at 949-631-1291.