Long-term plans to remove surface water from the sewer network are being drawn up by utility chiefs, but they stressed it has to be affordable.

Steve Wilson, Dwr Cymru/Welsh Water’s managing director of wastewater services, told a meeting of Swansea councillors and other public sector representatives that doing so was its biggest challenge in the coming years as climate change led to periods of more intense rainfall, which causes surface water flooding.

During these events, a mixture of surface water and sewage is frequently sent through storm overflow pipes into rivers and the sea, affecting water quality. In extreme cases, it can overwhelm the network and flood homes and businesses.

Mr Wilson said the “dreaded storm overflows are operating more frequently than we would like”.

He added that there was now a requirement for water companies in Wales and England to plan long-term to manage drainage and wastewater, as they have done for decades in resource terms, to ensure there was enough water to go round and accommodate growth.

He said “green infrastructure” – planters and trees, for example – and other sustainable drainage methods were the only way surface water could be absorbed, as removing Wales’ network of storm overflow pipes was not economically feasible.

“All of this has to be put on the water bill,” he told the Swansea public services board joint committee meeting. “It has to be affordable.”

Mr Wilson said Wales had 2,300 storm overflow pipes, and that removing them would add £11,500 to all of Dwr Cymru/Welsh Water’s 1.3 million customers’ bills.

He said rainfall patterns were changing. Wales, he said, was usually on the receiving end of one, two or three one-in-50-year rainfall events annually.He added: “We are heading for four or five, and climate change modelling tells us six or seven by 2050.”

He said a public consultation on the new drainage and wastewater management plan would start next month.

The UK Government said last month that water companies would face strict limits on when they could use storm overflows and must completely eliminate the harm any sewage discharge caused to the environment.

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