What does 'make-up water' refer to in boiler systems?

'Make-up water' in boiler systems specifically refers to the water added to the boiler to replace water that has been lost due to steam generation or leaks. Boilers operate on a closed-loop system where some water is inevitably lost when steam is produced and vented from the system. Additionally, leaks in the system can result in water loss. To maintain effective operation and ensure that the boiler has the appropriate water levels for optimal performance, it is necessary to add make-up water.

This process is crucial for maintaining the balance and efficiency of the system, as well as preventing problems such as overheating or damage due to low water levels. Properly managing make-up water is essential to ensure that the boiler continues to function safely and effectively. The other choices fail to define make-up water accurately; for example, cleaning and testing efficiency involve different processes unrelated to the concept of replenishing lost water in a boiler system.