A scheme that rewards farmers for reducing the amount of polluting run-off which washes from fields into rivers should beconsidered, a Dwr Cymru Welsh Water director has said.
Steve Wilson said he believed the idea had merit and that it would be brought up at this month's Royal Welsh Show as part of a discussion about problematic river catchment areas where new developments are on hold.
Mr Wilson also felt planning controls should be considered to make it harder for householders to Tarmac their drives, which contributes to more surface water entering the waste water network.
He was speaking to the Local Democracy Reporting Service ahead of a consultation about a new Welsh Water drainage and wastewater management plan - a long-term strategy to reduce the amount of times wastewater and sewage ends up in rivers and the sea. Councils and other organisations which own drains will be expected to participate fully.
Mr Wilson, Welsh Water's managing director of waste water services, said combined storm overflow pipes which sent surface water and sewage into rivers and the sea were operating "far more frequently" than it would like.
"Pressure is quite rightly on water companies to sort it out," he said.
Mr Wilson said any interventions would cost money, and that the Welsh Water had already committed to £800m of environmental improvements over the next five years.
He said everyone had a role in reducing surface water, including householders who added to the problem by covering drives with Tarmac and concrete or replacing lawns with artificial ones, thereby preventing rain from soaking into the ground.
Asked he supported the introduction of planning controls for such projects, Mr Wilson said: "Yes, I think there is a need. Everyone wants to see river water quality improved. Actually we all have a part to play - it's not just down to water companies."
He said new developments had to separate surface water from sewage pipes from the outset. What was harder, he said, was intervening in built-up areas, with Llanelli a case in point.
Mr Wilson said more surface water used to enter the sewer network in the Carmarthenshire town than its much bigger neighbour across the Loughor bridge, Swansea, before a £116m Welsh Water project.
This was a legacy, he said, of Llanelli having a higher concentration of terraced streets and fewer green areas compared to Swansea.
The RainScape project diverted surface water from the sewer network in Llanelli via a large pipe running eight metres under Station Road and into the estuary. Shallow channels of vegetation, called swales, were installed to soak up water. Upgrades were also carried out at nearby Gowerton.
Mr Wilson said combined storm overflow pipes in Llanelli now operated 10 to 20 times a year, compared to 60 to 80 - sometimes more - prior to RainScape, and that water quality in the estuary had improved. Eradicating all storm overflow discharges, he said, would literally involve intercepting rainwater at every individual property.
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Combined storm overflows act as relief valves during heavy rain, preventing homes and businesses from being flooded, although in severe instances the system can become overwhelmed.
Mr Wilson said Wales usually experienced one, two or three one-in-50-year rainfall events per year, but this is increasing due to climate change to four or five and potentially six or seven by 2050. This rainfall intensity has to be factored into the long-term drainage and wastewater plan.
Conversely, warmer and drier and summers can compound pollution damage to rivers because there was less water in them to dilute it.
Mr Wilson said Welsh Water worked well with councils which were badly affected by Storm Dennis in February 2020, and that it had a "fantastic" relationship with Cardiff Council.
Swansea Council, he said, "has been a little bit harder but by no means the worst".
He added the ownership of drains, pipes and culverts was fragmented, with councils owning some for example. He said it wasn't uncommon for car parks to be connected to the sewer network although they shouldn't be.