Why are approved backflow devices recommended to be installed above grade level?

Approved backflow devices are recommended to be installed above grade level primarily to prevent the relief port of the device from ever becoming submerged. This is crucial because if the relief port is submerged, it can allow contaminated water to flow back into the potable water supply, negating the purpose of the backflow prevention device. By ensuring that the device is elevated, it maintains a dry relief port, thus protecting the drinking water system from potential backflow contamination.

While considerations such as maintenance ease and inspection access are also important, they are secondary to the fundamental goal of the backflow device, which is to maintain a barrier against contamination. An installation that keeps the relief port above grade enhances the reliability of the backflow prevention, ensuring public health safety.