What condition could result from operating a fire pump in excessively hot water?

Operating a fire pump in excessively hot water can lead to decreased capacity. This situation arises because hot water can affect the physical properties of the water itself, leading to changes in its density and viscosity. As the water temperature increases, its density typically decreases, which means that the water becomes less effective at creating the required lift and flow necessary for optimal pump operation.

In this context, if the pump's design parameters are not suited for higher temperatures, the efficiency can drop significantly, resulting in reduced capacity to deliver the required flow of water. Fire pumps are designed to operate within certain temperature limits for optimal performance, and exceeding these limits can hinder their operational effectiveness, potentially leading to a less effective firefighting capability. Thus, decreased capacity is a direct consequence of operating under these challenging conditions.