Why Site Dewatering Matters
Groundwater, surface water and rainfall can stop a groundworks programme in its tracks. Flooded trenches cannot be worked in. Waterlogged excavations delay concrete pours, steelwork installation and backfilling. Foundation work beneath the water table requires continuous pumping just to maintain access. For groundworks contractors, dewatering is not optional — it is a direct enabler of programme progress.
Despite its importance, dewatering is still handled in many contractors' operations the same way it was decades ago: a submersible pump, a hose run to an outfall or soakaway, and one or more operatives managing the system throughout the working day.
Understanding Site Dewatering
Site dewatering covers any process that removes water from an excavation, trench or working area to allow safe and productive construction activities. Common applications include:
- Trench dewatering — removing groundwater from utility or drainage trenches to allow installation
- Excavation dewatering — pumping water from deep excavations, particularly below the water table
- Surface water removal — clearing rainwater and surface run-off from working platforms and temporary roads
- Footing dewatering — removing water from foundation bases before concrete is poured
- Flood event response — pumping following extreme rainfall events that overwhelm drainage capacity
Dewatering Equipment Types
Submersible Pumps
The most common form of site dewatering equipment. Submersible pumps are placed directly in the water being pumped, requiring hose runs from the pump to the discharge point. They require separate power sources (mains or generator) and typically need an operative to monitor and manage the system.
Wellpoint Systems
Used for large-scale dewatering below the existing water table. Wellpoints are installed in a ring around the excavation to draw down groundwater before work commences. Typically the province of specialist dewatering contractors.
Self-Contained Dewatering Units
A newer category of dewatering equipment that combines the pump, storage tank and support infrastructure in a single unit. The MW Equipment WetBag is an example: a 2,000L tank, 3-inch dirty water pump, diesel or hydraulic drive, and integrated hose storage in one relocatable unit — repositioned by the site excavator without mains power.
The WetBag reduces trench and excavation dewatering to a single-operator operation. No hose infrastructure across site, no mains power, no secondary machine. 80% faster pumping of footings and bases vs traditional methods. Learn more about the WetBag →
Environment Agency Compliance
Discharging pumped water on or from a construction site is a regulated activity. The Environment Agency's position is that water pumped from construction sites — which may contain silt, hydrocarbons, concrete washout or other contaminants — must be discharged to the correct point and at a quality that meets permit conditions.
Standard groundworks activities typically fall under an exemption or a water discharge activity permit, depending on volume and discharge point. Contractors should:
- Check whether their site activities are covered by an existing exemption (e.g. EA regulatory position statement for construction site dewatering)
- Obtain a water discharge permit where required for higher-risk activities
- Ensure pump outfalls are to a suitable receiving watercourse, surface water sewer or soakaway — not to foul sewer
- Maintain records of dewatering activities, volumes and discharge points
The WetBag's 2,000L storage tank is directly relevant here: it allows water to be stored and transported to an approved discharge point when no suitable outfall is immediately available — a common situation on urban and brownfield sites.
Reducing Dewatering Labour
Traditional dewatering operations typically require 2–3 operatives to manage pump setup, hose deployment, monitoring and relocation. The WetBag reduces this to a single operator: the excavator or telehandler that's already on site. Labour saving = men saved × machine hours × labour rate — for two men saved over an 8-hour day at £24/hour, that's £384 saved per day.
Across a 250-day programme, this amounts to £96,000 in saved labour — from a product retailing at £6,995. Use our ROI Calculator to calculate the saving for your specific operation.