Any water pump which takes suction from a public supply is generally considered a booster pump; however, the important distinction is whether or not the pump in question is a dedicated pump for the water-based fire protection system.......if the answer is yes, then NFPA considers the pump a fire pump (regardless of the source).
The legal aspect of pumps, and the acceptable arrangements, also changes depending on the system design (NFPA 13 or NFPA 13R or NFPA 13D)..........your options change depending on the applicable standard. Research and time my friend.