Public water systems across Colorado are committed to protecting their customers from backflow of contaminants into the drinking water system from cross connections. Backflow occurs when water flows in the wrong direction and can introduce contaminants backward into a potable water system and contaminate the water. The contaminated water can come from a connection with a non-potable contamination source (like a car wash, boiler or non-residential irrigation system). These connections are called cross-connections. Contaminated drinking water from cross-connections is a public health risk and must be prevented. All public water systems must comply with Colorado’s Primary Drinking Water Regulations, which contains a specific rule to prevent backflow. This rule helps protect customers by making sure that backflow prevention assemblies are installed and tested annually. Customers also have a role in helping keep drinking water safe from backflow.