Severn Trent said the problem affecting Ysgol Bro Ddyfi in Machnylleth was down to a burstpipe, and 45 people had phoned to complain that they had no water.
And on Monday a burst in a parallel pipe flooded the road, close to the entrance of St Peter's Hospital, forcing traffic to take a detour for several hours and leaving householders in the area temporarily without water.