Marcio,
O.K., the information you have obtained now is very helpful and has told me the supply arrangement to your home.
The nominal 127-volt level was quite common throughout Continental Europe years ago (including Portugal, which probably accounts for its use in Brazil).
The fact that you have 220 volts available indicates that you have what is known as a 3-phase supply. These are very rare for residential use in America or Britain, but again, quite common in Europe.
Coming into your house from the street will be 4 wires: 3 phases (hot/live wires) and a neutral. Between any phase and neutral the voltage is 127V. Between any two of the three phases, you get 220V.
So for a shower designed or wired for 127V operation, it would be connected between one phase and neutral. For a shower wired for 220V use it will be connected across two phases.
The advantage of the 220V version is that for the same amount of power (watts), you need less current, so the cables can be smaller.
As for grounding each shower to its own rod, this would be effective only if the shower is fed through a device known as either a GFI (Ground Fault Interrupter) in the U.S.A., or an RCD (Residual Current Device) in the U.K. (I'm sorry I have no idea what it would be called in Portuguese.)
Without such a device, you could not get enough current to flow through the ground to blow a fuse or operate a normal circuit-breaker.
Such local grounding of a shower may be against your wiring rules (if you have any in Brazil?), but that aside it is a rather inelegant solution to the problem.
I would strongly advise you to have the showers grounded back to the main panel.
