One of the most pressing questions facing the water sector in 2026 is ‘how to prevent sewage water pollution.’ On the surface, the answer is infuriatingly straightforward. Water pollution caused by sewage could be reduced when less unwanted flow enters the sewer network, more wastewater is carried forward for treatment, and assets are maintained so they perform as intended during variable hydraulic conditions.
For an individual network, however, the reduction route depends on the pathway creating the pollution. For example; surface water entering combined sewers, groundwater infiltration consuming capacity, blockages restricting flow, pumping assets underperforming, treatment headroom being exceeded, or misconnections allowing foul flow to reach surface water drains.
That is why “how can water pollution caused by sewage be reduced” is too broad as a single engineering question. Full prevention may not be realistic across every operating condition, but targeted reduction is possible when the hydraulic, mechanical and treatment constraints are understood. Read on as we unpack the issue.
One route to reducing sewage pollution is to limit the volume of non-foul water that enters the wastewater network in the first place. In combined systems, road and pavement drainage, roof drainage, paved commercial areas and groundwater ingress can all occupy capacity that would otherwise be available for foul flow and onward transfer to treatment.
The practical value of surface water separation, sustainable drainage systems, permeable construction and rainwater capture is that they can change the timing, peak rate and total volume entering the sewer. Where hydraulic load is reduced upstream, downstream assets have a better chance of maintaining pass-forward performance without reaching overflow or surcharge conditions as quickly.
Infiltration occurs when groundwater enters the sewer through defective pipes, joints, laterals, chambers or manholes. The water may be relatively low in pollutant concentration compared to untreated sewage, but is problematic because it occupies capacity continuously or seasonally, depending on the groundwater level and asset condition.
High infiltration can leave your network partly loaded even before rainfall begins. It can also increase pumping hours, reduce spare storage capacity, and dilute wastewater reaching treatment processes. Sewer inspection, flow monitoring, night-flow analysis and targeted rehabilitation help identify whether infiltration control will reduce the hydraulic pressure behind sewage pollution risk.
In networks where wastewater has to be lifted, screened or transferred before treatment, pollution reduction depends on the assets holding their operating performance under changing flow conditions. A pump station that loses transfer rate through ragging, worn impellers, level-control faults, poor duty/standby changeover, blocked screens, valve defects or rising-main restriction can reduce the amount of wastewater moving through the intended route.
That loss of performance changes upstream hydraulic conditions, so that wet wells fill faster, upstream storage is consumed earlier, and the network has less tolerance when additional flow arrives. Your service records, telemetry, alarm history and pump run data should therefore be reviewed together to identify whether mechanical condition, controls or downstream restriction is contributing to sewage pollution risk.
Blockages and deposits change how wastewater moves through the network. Fats, oils, grease, wipes, silt and root ingress can reduce pipe area, slow flow, increase upstream levels and create local surcharge conditions. In some locations, this restriction can be the immediate cause of a pollution incident even where the wider system has adequate design capacity. Planned cleansing, root cutting, blockage analysis and targeted pipe repairs are therefore pollution-reduction measures when they restore conveyance through a critical sewer length.
To find out more about reducing the sewage water pollution risk across your wastewater assets, please speak to one of our experts today by clicking here.
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