What mechanism must a drip irrigation system include?

A drip irrigation system must include a backflow prevention device to ensure safe and effective operation. This device prevents contaminated water from flowing back into the potable water supply, which is crucial to protect public health and maintain water quality. Drip irrigation systems operate under low pressure, and the introduction of contaminants can occur if there is a drop in supply pressure or other issues that lead to backflow. By incorporating a backflow prevention device, the system adheres to safety standards and regulations, ensuring that no harmful substances can inadvertently enter the water supply.

The other mechanisms listed, while they may be important in other contexts, do not specifically address the critical need for backflow prevention. For example, a manual valve may control water flow, but it does not prevent contamination. Similarly, mechanisms for flushing from the drainfield back to the treatment unit or pump tank and pressure release valves play roles in managing water flow and pressure but do not ensure that backflow of contaminated water is prevented, which is a primary concern for maintaining system integrity and public safety.