PLUMBING & DRAINAGE
WHEN IT RAINS, IT POURS
Surface water inflow into foul water systems is a longstanding issue that continues to strain sewage infrastructure all over the country.
A
larming statistics from the latest Water Industry Specification (WIS) underscore the scale of this problem impacting surface water inflow into foul water systems, straining sewage infrastructure across the country. The report revealed that a single 600x600mm double triangular cover, even within the manufacturing tolerances of industry standard EN124, was found to admit up to 22 litres of water per second under certain conditions - this is equivalent to the design peak foul flow from 475 homes.
Wrekin Products technical development and specification manager Paul Thompson says that even at a mere 5mm immersion
depth, such covers can admit more than three litres per second. “Given that most of the water company’s small “foul-only” pumping stations have a capacity of around 11 litres per second, this represents a significant risk of overloading sewer systems, causing flooding, environmental contamination, and escalating costs for treatment and pumping” he says. Raw sewage entering rivers and seas remains a massive environmental concern, impacting both aquatic life and human health. Environmental groups continue to sound alarms over the devastating effects of pollution, including fish deaths and contaminated drinking water.
Environmental costs The impact of untreated sewage entering waterways is extensive. Water companies are regularly fined for failing to meet legal obligations, and the economic cost of environmental damage, coupled with the public health risks, is immeasurable. Thompson adds: “As pressure to tackle sewage overflows and leakage intensifies, the government has mandated that water companies install monitoring systems on all storm overflows. However, this is just one part of the solution. Another major contributor to pollution is the leakage of surface water into foul sewer systems via manhole covers. This leakage can dramatically increase the flow of untreated water into already burdened systems, overwhelming pumping stations and treatment plants. The challenge lies not only in managing sewage overflow but in addressing the more subtle, but equally damaging, surface water infiltration.”
As part of the effort to mitigate these 34
issues, water companies have increasingly turned to improved manhole covers with low-leak specifications. The WIS includes a comprehensive approach to measuring the leak tightness of these covers, assigning a classification from 0–3 based on their performance in restricting surface water inflow. “The adoption of low-leak manhole covers is not just a regulatory requirement but also a cost-effective, long-lasting solution that benefits water companies and the environment alike,” he adds. Providing solutions that offer this type of technology, such as retrofittable high-performance seal plates that reduce the ingress of surface water into sewer networks ensures that water companies are not treating unnecessary surface water.
The latest Environment Agency data highlights the urgent need for action to address waterway pollution, which is a growing environmental and public health crisis. The legal, economic, and ecological implications of failing to control surface water infiltration into foul sewer systems cannot be overstated. However, the adoption of proven, low-leak technologies offers a sustainable, cost-effective solution.
“Through innovation, industry collaboration, and the implementation of WIS-compliant products, water companies can build more resilient sewerage networks that reduce the risk of flooding and environmental damage while improving operational efficiency,” explains Thompson. “With the right solutions, the water industry can not only meet its regulatory obligations but also create a more sustainable future for both the environment and communities.” BMJ
www.buildersmerchantsjournal.net February 2025
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