Most espresso machines have a maximum water pressure of 4 to 6 bars. If you can't plumb water to the machine, it is a good idea to pre-pump water from a reservoir to pressurized holding tank. Then connect the tank to the machine or just pump straight to the espresso machine.
You can just hook a hose to your espresso machine pump and put the other end in a water tank. But from what I have seen the pump wares out a lot faster.
Nuova Simonelli is a good machine, but so is La Cimbali.