How many gallons of water does the backwash water tank hold?

The correct answer indicates that the backwash water tank has a capacity of 20,000 gallons. This high capacity is essential for the efficient operation of water treatment systems, particularly in those that require significant volume for backwashing filters and other maintenance activities. A large tank allows for adequate storage and ensures that there is enough water available for the backwash process without interrupting service or requiring frequent refills.

In water treatment systems, the backwashing process typically involves reversing the flow of water through filters to remove accumulated debris and contaminants, thus maintaining the effectiveness of the filtration system. Therefore, having a backwash water tank with a capacity of 20,000 gallons helps to facilitate this process effectively, minimizing downtime and ensuring water quality.

The other options represent lesser capacities that would be insufficient for comprehensive backwashing needs, which can vary based on system size and the level of contaminants being filtered. Thus, the choice of 20,000 gallons is aligned with the operational requirements of such systems.