Vandals have opened fire hydrants in several areas in Coventry.
Streets in the Bell Green, Longford and Keresley areas were targeted overnight on Wednesday releasing gallons of water and leading to low pressure.
Severn Trent said it is not thought there is any contamination but a spokesman claimed workers were attacked as they tried to shut the water off.
Fraser Pithie, from the firm, said his staff worked "through the night" to try to shut them down.
He has apologised to customers for the inconvenience.
"If you start opening fire hydrants upon our network, you start to lower the pressure quite considerably and you waste a lot of water.
"We think about our staff who, throughout the night, have been out trying to shut these things down and as soon as they shut one down the idiots have opened another one somewhere else."