Whenever I leave home or the appartment I turn off all the water. In the UK this is to limit the damage if we get a freeze-up and burst, but in Spain the damage caused by a small leak can be considerable because of the time the place is empty. We are in Mar y Sol, but all these apartments are on mains supply, so turning the small lever valve (usually built into the wall near the water heater) will stop all water entering the appt. The 2 small tap headed valves by the water heater simply turn off the hot water via the heater and not the cold to the rest of the appt. and are used to isolate the water heater in case of problems. faulty pressure relief valves are common, ours squeeks loudly every time a tap is turned off and the pressure builds up, but so far no leaks, but by turning off the main cack whilst we are away at least I will be there if there is one,
Mike