If an MWS apparatus is equipped with a fire pump, it is referred to as a...

When an MWS (Mobile Water Supply) apparatus is equipped with a fire pump, it is referred to as a tanker-pumper. This designation is significant because it highlights the dual functionality of the vehicle: it is both capable of transporting water (as a tanker) and of pumping that water under pressure to extinguish fires (as a pumper). The presence of a fire pump enables the tanker-pumper to deliver water at a necessary pressure for effective firefighting operations, making it a versatile and essential tool in fire service for rural and urban environments where water supply may be limited.

The other options do not accurately reflect this dual function. A water-tender typically refers to a vehicle that is primarily focused on transport rather than having a significant pumping capability. A pressure-pumper highlights the pumping capability but does not specifically indicate that it also serves as a water transport vehicle. Lastly, a reservoir-pumper suggests a specific water source application, which is not the primary characteristic of an MWS apparatus with a fire pump. Thus, tanker-pumper is the most precise term used in this context.