NORTHUMBRIAN Water's telephones were red hot following a fractured main in Darlington - but hundreds of callers received no response.

Yesterday the water watchdog, Northumbria customer service committee, heard that a contractor employed by Darlington council caused the damage, despite having been shown the main's location.

The incident happened at 8.30am on September 8 and had the potential to affect 22,500 properties in the north-west of the borough. The repair was almost complete when the crew discovered a valve had not closed properly, spreading the problem further east.

But ten staff at Northumbrian Water's call centre were unaware that the discoloured water problem had escalated.

Mr Ivan Jepson, customer services manager, said up to 700 calls an hour were being received at one point. "At the peak time I would have needed 140 people in the room taking calls. Between 5pm and 9pm the lines were red hot."

The majority of the callers received a recorded message telling them to try again later.

"It was a pure human mistake that the operations supervisor failed to notice the build-up of traffic," added Mr Jepson.

The supply was back to normal by 1am the following morning.

Mr Jepson said Northumbrian Water had since spent £500,000 on new technology. It could now put out recorded messages explaining what was happening in affected areas

It also had an emergency back-up from a Leicester call centre with 100 staff on tap.

Mr Graham Neave, customer service director, said its water sampling practice had been altered after criticism from the Drinking Water Inspectorate, which said testing should have been done more immediately.

Committee chairman, Andrea Cook, concluded: "It is quite evident that people are not perfect - whether it was the contractor or the person in the call centre. But you have taken action to remedy the situation."

Mr Peter Marsden, an inspector, told the D&S Times: "Although the water looked pretty disgusting, there was no threat to public health."