Civil Engineering Wastewater Design and Sewer Adoption
Delivering efficient wastewater infrastructure. SWJ Consulting provides expert design and technical support for wastewater design & sewer adoption for foul and surface water drainage systems — from initial concept to final adoption.
Design Standards and Guidance
All of our wastewater and drainage designs adhere to the latest national standards and technical guidance to ensure regulatory compliance and long-term system performance.
Our designs follow:
- Sewer Sector Guidance (SSG) – setting the criteria for design, construction, and adoption of sewers and pumping stations by water authorities.
- Building Regulations Part H – covering the design, capacity, and installation of foul and surface water drainage systems within property boundaries.
- CIRIA SuDS Manual (C753) – providing best-practice principles for sustainable surface water management, ensuring designs reduce runoff, improve water quality, and enhance site resilience.
By aligning every project with these standards, SWJ Consulting ensures that both adoptable and private drainage systems are efficient, durable, and environmentally responsible. By working closely with local water authorities and developer services teams, we streamline the approval process and minimise costly redesigns or construction delays.
Adoptable Drainage Design – Design of Foul and Surface Water Sewers
Effective wastewater design begins with the separation and routing of foul water (from toilets, kitchens, and bathrooms) and surface water (from roofs, roads, and paved areas). SWJ Consulting designs both systems to ensure safe conveyance, capacity efficiency, and long-term reliability.
We use advanced hydraulic modelling and digital design tools to determine optimal pipe routes, gradients, and sizing to prevent surcharge and flooding during extreme rainfall events. With efficient earthworks and coordination with other site infrastructure such as highways, utilities, and SuDS features, we look to optimise value and minimise our client’s construction costs.
Adoptable Drainage Design – Design of Foul and Surface Water Sewers
Effective wastewater design begins with the separation and routing of foul water (from toilets, kitchens, and bathrooms) and surface water (from roofs, roads, and paved areas). SWJ Consulting designs both systems to ensure safe conveyance, capacity efficiency, and long-term reliability.
We use advanced hydraulic modelling and digital design tools to determine optimal pipe routes, gradients, and sizing to prevent surcharge and flooding during extreme rainfall events. With efficient earthworks and coordination with other site infrastructure such as highways, utilities, and SuDS features, we look to optimise value and minimise client’s construction costs.
Rising Mains and Pumping Stations</h2
When gravity flow is not feasible — for example, on flat or low-lying sites — pumping stations and rising mains are used to transfer foul or surface water to a higher-level outfall or main sewer.
We can complete:
- Hydraulic design of rising mains.
- Pumping station layout, capacity sizing, and pump selection
- Wet well and valve chamber design in accordance with water authority standards
- Integration with telemetry and control systems for operational monitoring
We work closely with mechanical and electrical engineers where required, ensuring the system is both energy-efficient and adoptable under Sewer Sector Guidance (SSG).
Technical Vetting and Approval Coordination
Before a drainage system can be adopted, the design must undergo technical vetting by the local water authority or their appointed engineer. We will act as the client’s representative during this process to provide responses to technical queries and clarifications, coordinate between design, contractor, and authority teams and help to maintain approval timelines. Our detailed knowledge of authority-specific requirements allows us to resolve issues quickly and secure technical approval efficiently.
Section 104 (S104) submissions and liaison with water authorities
To have a new sewer adopted by a local water authority, a Section 104 Agreement (under the Water Industry Act 1991) must be in place. This legal agreement sets out the design, construction, and maintenance requirements for the system before it is transferred to the authority for ongoing ownership.
We can help you manage the S104 process from start to finish, including preparation of the full S104 submission pack (drawings, calculations, specifications, and schedules). Liaising directly with developer services teams at the relevant water authority. We will be on hand to respond to any technical comments and revise designs, if necessary, as well as coordinate the construction inspections and final approval.
Working with SWJ Consulting for new sewer adoption will reduce delays in the approval process and help clients achieve timely sign-off before project completion.
As-Built Drawings and Adoption Certification
Once construction is complete, accurate as-built drawings and supporting documentation must be submitted to the adopting authority. These confirm that the works were built in accordance with the approved design and meet all testing and inspection standards. We can prepare the as-built and record drawings (including manhole schedules and invert levels), any CCTV surveys and testing certificates, all maintenance and operational information and the final documentation required for the adoption certificate and transfer of responsibility. This information is also used for the O&M Manuals if required for building handovers etc.
This final stage ensures a smooth handover from developer to authority and confirms that the drainage system is compliant, safe, and ready for long-term operation.
Private (Non-Adopted) Drainage Design
Not all drainage networks are intended for adoption. For private developments, industrial estates, or rural properties, SWJ Consulting provides robust, compliant private drainage designs that perform efficiently and meet environmental and Building Regulation standards including Building Regulations Part H, BS EN 752:2017 – Drain and Sewer Systems Outside Buildings, CIRIA SuDS Manual (C753) and the Environment Agency Guidance for discharges and treatment.
Our private drainage expertise includes:
- On-site foul and surface water systems
- Sustainable drainage (SuDS) design and integration
- Soakaways, attenuation tanks, and treatment plants
- Drainage strategy reports to support planning applications
- Septic tanks and package treatment plant design to Environment Agency
Why choose SWJ Consulting?
- Specialist Knowledge: Proven experience in both adoptable and private wastewater design across residential, commercial, and mixed-use developments.
- Streamlined Approval: We liaise directly with local authorities and statutory undertakers to secure timely approvals.
- Integrated Design Approach: Coordination with structural, highway, and flood risk teams for efficient, holistic project delivery.
- Trusted by Developers: Our designs are consistently accepted first time by adopting authorities, reducing time and cost for our clients.
If your project requires sewer adoption or a private drainage solution, get in touch with our civil engineering team who can guide you through the design and approval process from start to finish.
