The Environment Agency is warning water companies to improve their performance on pollution after serious incidents rose to 120 in 2011, up from 65 in the previous year.

The almost twofold increase contrasted with an overall 4% decrease in serious pollution incidents year on year, the Agency’s Sustainable Business Report, published today, reveals.

Most incidents occurred within the sewer or water network, while only 19 were from permitted sites such as sewage treatment works.

The Agency said it is working with water firms to establish the cause of the increase and is encouraging them to report pollution incidents themselves. There has been a steady rise in the number of incidents reported by water and sewerage companies in recent years, and the percentage self-reported increased slightly to 63% in 2011.

There were 620 serious pollution incidents in 2011, 240 of which were from permitted sites. Of these, 120 were from water company owned sites and 101 from sites involved in waste activities.