What does "makeup water" refer to in a boiler system?

Makeup water refers specifically to the water that is added to a boiler system to replace losses that occur due to evaporation or blowdown. In a boiler operation, water is continuously lost through steam generation and is often removed intentionally through a process called blowdown to control the concentration of impurities in the boiler water. As these losses occur, it is essential to maintain the required water level and system performance by adding makeup water, which helps ensure the boiler operates efficiently and safely.

Other choices may pertain to different functions within a boiler system, but they do not accurately define makeup water. For instance, flushing the system does not directly relate to ongoing operational losses, enriching fuel pertains to fuel composition rather than water handling, and emergency shut-off involves safety mechanisms rather than routine water management. These distinctions make it clear that option B is the appropriate choice for understanding the role of makeup water in a boiler system.