Over three thousand Severn Trent customers cautioned against using water supply due to abnormal chlorine levels. Getty Images

Over three thousand Severn Trent customers across parts of Derbyshire and Leicestershire have been warned against using their water supply due to abnormal chlorine levels. Customers with postcodes falling within the range of DE11, DE15, DE65, DE73 and the LE65 were cautioned by the water company in a statement.

"We're sorry for the inconvenience this will cause and we're working hard to isolate the problem and get everything back to normal as quickly as possible," said the company in a statement. The precautionary statement also advised customers against flushing their toilets until further notice.

The warning comes after the company noticed "a problem with higher than normal levels of chlorine" at the water company's Castle Donington reservoir. Severn Trent employs a filtration process using chlorine to allow for the water supplied to be clean enough for drinking. The problem was discovered through a monitoring system alarm. A total of 3,560 properties were found to be affected.

Meanwhile, a number of residents have complained that the company did not do enough to warn the customers ahead of time. "The smell from the dishwasher was extremely strong of chlorine. It smelt a little like a swimming pool... I've got a son who is poorly...It means we can't give him any cool water, we can't wash his clothes. We can't shower or bathe him to help cool him down," resident Owen Pritchard from Chellaston told Sky News.

So far, Severn Trent has not said how long it will take before the issue can be resolved. "It looks like there's been over-chlorination...Once we've got through this incident and we've flushed the water through the system, we can go back, take a look and see exactly what happened," said a spokesman. "A Do Not Use notice means that customers shouldn't use their water supply for anything - including drinking, preparing food and bathing."