I was doing WCs and ran out of hot water when about to fill my MALs tank, so I turned off the water and waited for it to come back. Unfortunately, the faucet was on a tiny, tiny bit...enough so that when I came back in 30 minutes later the tank had topped up about 20% with freezing water! Fortunately the hot water was back, so I quickly warmed up the tank, and much to my relief, the lungs fine...D'oh!