Scottish Water sets out CSO ambition

Scottish Water has outlined plans to improve all combined sewer overflows (CSOs) that pose a risk to water quality across its 50,000km of sewer network as part of the company’s route map to improve urban waters.

The company has improved 279 CSOs since 2010 that were shown to impact water quality and will continue the work for the 3,614 CSOs across Scotland.

The Urban Water Improvements route map was designed to improve water quality; monitor and report on discharges from all CSOs; reduce sewer related debris in the environment; and reduce spills from the sewer network.

Upgrading the entire sewer network to eliminate spills from CSOs is estimated to cost £13 billion, while improving water quality and removing sewer related debris is expected to cost £1 billion.

Improving water quality would be done via a combination of reducing unflushables entering the network, removing surface water from the network, adding extra storage capacity, and screening where spills are predicted to occur. Scottish Water said it would find opportunities to remove surface water before increasing storage.

CSOs with the most significant impact on the water environment will be prioritised.

The first phase of work, which runs to 2024, will include installing monitoring equipment in the network and at treatment works of approximately 1,000 priority CSOs to improve the company’s understanding of how they are operating. From this information the company will determine what the next steps need to be.

The costs and benefits of adding monitoring to around 2,600 low priority overflows where spills are not believed to be occurring or causing environmental impacts will be assessed.

By 2024, the company will publish near-time spill data for all monitored CSOs, with data from those currently monitored to be published by the end of this year.

Sensors will be added to the wastewater network to generate insights on the state of the sewers that will allow staff to take proactive measures to avoid blockages and better understand how dry weather as well as heavy rainfall affects the systems.

As part of efforts to control the non-flushable items that enter the network, Scottish Water will support government plans to ban single use plastic products including wet wipes and roll out an awareness campaign to customers about properly disposing of such items.

Following the first phase, the company will from 2027 onwards work to reduce spills from CSOs by maximising surface water management and deliver solutions for zero uncontrolled discharges in the longer term.