In a high riser building of about 100m height, a dry riser system is not visible as the firemen's vehicle can't pump water up to 100m. As such, av decided to have it as Wet riser. At same time I don't want introduce a separate pump to avoid over bloating of project cost. My sprinkler system must have finished fighting before I can think of using the wet riser, as such the sprinkler pump will be idle, can I use the sprinkler pump for the wet riser?Is there any fire regulation that says I can not use the same sprinkler pump as the wet riser pump? Must I increase the size of my dedicated fire water tank?

It best to check with your local fire dept (and insurance com); they do have sprinkler and wet pipe on the pump

AS per NFPA and most regional regulation, you CAN use one pump for sprinklers, stand pipe, hydrant and hose reel