Which type of valve allows for the flow of water in one direction only?

The choice of a check valve as the correct answer is based on its specific function, which is to permit flow in one direction while preventing backflow. This functionality is essential in various applications, particularly in wastewater management and collection systems, where maintaining the correct flow direction is crucial for system integrity and efficiency.

A check valve operates automatically, using the fluid's pressure to open itself when flow is present and then closing if the flow reverses. This is important in preventing contamination of clean water supplies or protecting pumps and other downstream components from damage due to backflow.

In contrast, the other types of valves mentioned—such as the butterfly valve, plug valve, and gate valve—are primarily designed for flow regulation or shut-off purposes, rather than for backflow prevention. Butterfly valves and gate valves can control flow but do not inherently prevent it from reversing, while plug valves can also provide flow control but share similar limitations regarding backflow. Therefore, understanding the purpose and operational mechanics of a check valve highlights why it is the appropriate choice for this scenario.