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DropSeal: stopping infiltration at source without locking networks in

04 August 2026
Paul Thompson
Paul Thompson

Technical Specification and Sustainability Manager

 

Surface water entering foul-only networks remains a hidden but significant issue. Even shallow ponding over standard manhole covers can introduce flows large enough to overwhelm pumping stations, increase energy use and reduce treatment capacity for genuine wastewater.

Independent Water Industry Specification testing has shown that a single 600 × 600 cover, within EN 124 tolerances, can admit flows equivalent to the peak foul load from hundreds of properties. That is before prising slots and keyways are considered.

For asset owners, this presents a clear challenge. How do you reduce infiltration without introducing permanent, inflexible solutions that compromise access, safety or future decision-making?
 

Sealing as a Performance Outcome, Not a Fixed Accessory


Both Sewers for Adoption and Sewer Design and Construction Guidance consistently refer to the need to control infiltration and manage network performance. What they do not do is prescribe specific cover-level sealing devices or mandate permanent secondary components.

That distinction matters. Sealing is treated as a performance outcome. When additional measures are used, they are justified by site conditions and operational risk, not by blanket compliance.

 

 

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A different approach to sealing

DropSeal has been developed around this principle.

Compatible with selected Highway and Unite manhole-cover systems, DropSeal uses a push-fit ductile iron seal plate that locates directly within an integrated receiving feature in the frame.

This avoids bolted steel trays and separate secondary subframes while maintaining the full clear opening for chamber access. It also allows sealing to be added, upgraded or removed throughout the asset's lifecycle without replacing or reinstalling the frame.

Crucially, sealing does not have to be installed on day one.

Once a compatible frame is in place, seal plates can be added, upgraded, removed or redeployed as network priorities change. This gives operators the flexibility to adapt sealing performance as network requirements evolve and investment priorities shift.

Find out more about DropSeal

Leak-Tightness Performance Tested to WIS Criteria

Different locations demand different responses.

DropSeal offers leak-tightness performance options tested in accordance with WIS 4-26-01 criteria, helping operators select the most appropriate approach for site-specific risks and operational requirements.

This allows sealing performance to be matched to network risk while maintaining flexibility throughout the life of the asset.

Designed for operation, not just installation

DropSeal has been developed with operational teams in mind:

  • The seal plate mirrors the cover’s BS7903 lifting key points
  • Indexed design ensures correct installation every time
  • Full clear opening supports safe and efficient man access
  • Seal plates can be reinstated after access or moved to new locations

Combined with the frame’s CD534-compliant design and FrameSet compatibility, this delivers a solution that works across installation, operation, and long-term asset management.

Targeted sealing. Long-term flexibility.

Network conditions rarely stand still.

As operational needs evolve, sealing requirements can change from one location to another. DropSeal has been designed to support that reality by allowing operators to modify sealing performance without the disruption and cost associated with replacing installed frames.

By avoiding permanent secondary systems and supporting redeployment where appropriate, DropSeal provides a practical approach to managing infiltration across a changing network.

DropSeal provides a practical way to reduce infiltration at source, protect network capacity and avoid unnecessary treatment of clean water.

Most importantly, it helps operators adapt sealing performance to the evolving demands of their network, without removing future choices.

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