Students at Goolwa Primary School, south of Adelaide, have been told to stay home as a major outage means there is no water available for flushing toilets.
SA Water said 7,000 properties at Middleton, Goolwa and Hindmarsh Island remained without water because of a pipe rupturing on Thursday night.
It said it might take much of Friday before the breach would be fixed and the water restored.
SA Water has supplied bottled water for south coast residents.
Goolwa Primary School's acting principal Kym Polker urged parents to keep students at home for now.
"We have water for drinking, bottled water available, but there's no water for flushing toilets so [it is] certainly an issue with health and safety," he said.