A new build £38m school told all pupils to work from home after a broken pipe caused flooding.
The re-built Pencoedtre High School in Barry only opened in January and all 1,000 pupils are learning from home on the first day back after half term.
A broken pipe caused extensive flooding on the first floor during the weekend which meant the mains water supply has had to be cut off, said headteacher Lee Humphreys.
