Water Supplies for fire pumps can either be pressurized or static.  They can also be private or public. 

Many fire pumps take suction from a captive supply, such as a tankThis "suction" tank is supplying two separate fire pumps in a warehouse. This is an above ground static supply, used for no other purpose than providing a supply for the fire pumps protecting the property., while others may be connected to a municipal supply, or other pressurized fire main that acts as the suction source for a pump.