Cross-Connection Control

Customers use water for many different purposes, and the water may come in contact with other substances not fit for consumption. This connection between clean water and other substances is called a “cross-connection.”


It is a logical assumption that because water is always under pressure, it can only flow in one direction. However, can it flow the opposite way from its intended direction? The answer is yes, and when it does, it can cause disastrous results. Water will always flow toward the point of lowest pressure.

If a water main in the public water system should break, or if a fire occurred and the fire department opened several hydrants, the water mains' pressure could drop dramatically, causing a reversal of flow. The potential for this reversal of flow is why Skagit PUD is concerned about the possibility of contaminants or pollutants being siphoned back into the water system.

When the plumbing at a residence is connected to the potable water supply and is connected to piping carrying another fluid or gas, such as an air conditioner containing chemicals to kill algae, the contaminant could be drawn back into our water mains. A garden hose submerged into a hot tub or swimming pool, or inserted into your car’s radiator to flush out antifreeze, or attached to a fertilizer sprayer, could siphon these contaminants back into our water mains. Incidents such as these have been documented throughout the country and have happened all too often.

Fortunately, backflow from a cross-connection can be prevented. Skagit PUD’s Cross-Connection Program protects the water system from contaminants by ensuring that customers have properly installed and maintained backflow prevention devices.

Call Cross-Connection Control at (360) 848-2138 for more information.

Frequently Asked Questions

What is Cross-Connection?
A cross-connection is defined by the Washington Administrative Code 246-290-490 as “any actual or potential physical connection between a public water system or consumer’s water system and any source of nonpotable liquid, solid, or gas that could contaminate the potable water supply by backflow."

What is Backflow?
Backflow is the undesirable reversal of the flow of water or other substances through a cross-connection into the public water system or consumer’s potable water system. There are two types of backflow—backpressure and back-siphonage.

What is Backpressure?
Backpressure means a pressure (caused by a pump, elevated tank or piping, boiler, or other means) on the consumer’s side of the service connection that is greater than the public water system's pressure and which may cause backflow.

What is Back-Siphonage?
Back-siphonage is backflow caused by a negative pressure (i.e., a vacuum or partial vacuum) in the Public Water System or consumer’s system. The effect is similar to drinking through a straw. Back-siphonage can occur when there is a stoppage of water supply due to nearby firefighting, a higher than normal water withdrawal rate, a break in a water main, etc.

What are Backflow Preventers?
Backflow preventers are mechanical devices designed to prevent backflow through cross-connections. However, for backflow preventers to protect as designed, they must meet stringent installation requirements.

Cross-Connection Standard Details

Skagit PUD has adopted standard specifications for the installation of backflow prevention assemblies.

See these standard drawings for more information:



Under current state regulations, the water purveyor protects the public water system from contamination via cross-connections. The water purveyor’s responsibility for cross-connection control begins at the water supply and ends at the point of delivery to the consumer’s water system, the water meter. The “Authority Having Jurisdiction” (e.g., City or County) is responsible for cross-connection protection within the consumer’s water system and property lines.

To protect the public water supply, Skagit PUD may require premise isolation of a facility. Appropriate planning should address the possible requirement of a Reduced Pressure Backflow Assembly (RPBA) or Double Check Valve Assembly (DCVA) to be installed immediately after any metered water service or fire service connection, now or in the future. DCVAs can be installed below ground with brass plugs in the test cocks. RPBAs are to be installed above ground with a minimum of 12-inches of clearance below the assembly to finish grade, and protected from freezing and abuse. If the RPBA is installed in an above-ground enclosure, the enclosure must have a drain opening adequately sized to handle the relief valve's maximum flow.

All backflow prevention assemblies are to be on the Washington State Approved List of Assemblies. Skagit PUD will require copies of the initial test(s) of the required backflow prevention assemblies. The owner will be responsible for subsequent annual testing and providing the test results to Skagit PUD.