Freinds of ours had a faulty main tap in their apartment block, when they had this changed the valve, inside was corroded so when they thought they were turning the water off at the main valve, to leave the apartment it was still running.
On the complex five people have now had the valves changed as a precaution and everyone was corroded inside and not working. It is worth turning you water off at the mains and checking it is off. These could have been a bad batch used 6 years ago they were cheap valves made in China.
Mark