Trade Effluent Licence For Construction Site Activities

All construction projects handle water, using it as a resource and handling it as a waste.

Planning and managing this accordingly to regulations and ethical responsibilities is increasingly important to prevent unexpected costs and delays occurring during the course of construction works.

On modern construction sites, water is used in a wide range of activities including dust suppression, concrete mixing, wheel washing and welfare facilities. At the same time, rainfall can accumulate on site, particularly during groundworks and early construction phases, creating large volumes of surface water that must be managed. Without a structured approach to managing trade effluent, these activities can quickly lead to compliance issues, programme delays and increased operational costs.

Many sites will need to discharge water into foul drainage to remove it from site. Doing so will require a specific trade effluent licence, and this whitepaper sets out the key areas and responsibilities contractors should be aware of.

What is a Trade Effluent Licence?

When looking at solutions for discharging your trade effluent, the public sewers are often the preferred option where it’s reasonable to do so. Strict requirements are put in place for this type of disposal, and under Section 118 of the Water Industry Act 1991, to discharge trade effluent through the sewers you are required to have a Trade Effluent Licence.

Defined by the Water Industry Act 1991, Trade Effluent is:

“Any liquid, either with or without particles of matter in suspension in the liquid, which is wholly or partly produced in the course of any trade or industry carried on at trade premises.”

On construction sites, this definition typically covers water generated through activities such as concrete works, equipment washing, ground stabilisation, drilling, and site drainage. Even rainwater that has come into contact with site materials can be classified as trade effluent, meaning it must be controlled before discharge.

Limiting values can be put on the volume, flowrate, pH, temperature, ammonia, Chemical Oxygen Demand (COD), suspended solids, toxic metals, and other factors of the trade effluent. These limits are put in place to ensure the discharge doesn’t interfere with the sewer companies’ usual activities, or cause harm to workers, the environment, or the wider public.

In practical construction scenarios, exceeding these limits can result in immediate operational consequences, including suspension of discharge permissions or enforcement action.

Trade Effluent Composition

Most trade effluent consists of liquid. This comes from water used in construction processes as well as rainwater that falls on or accumulates within the site.

On construction sites, this often includes runoff from exposed ground, temporary haul roads, excavation pits and material storage areas. This water may appear relatively clean but can contain contaminants that require treatment before discharge.

Liquid Phase

The sewer provider will place strict limits on the concentration of suspended particles present within the effluent. Suspended solids can cause infrastructure damage to the sewers or block pipes, disrupting normal operations.

On construction sites, suspended solids typically originate from soil, silt, clay and cementitious materials. Activities such as excavation, piling, cutting and vehicle movements can significantly increase suspended solids in water.

Suspended Solids

The sewer provider will place strict limits on the concentration of suspended particles present within the effluent. Suspended solids can cause infrastructure damage to the sewers or block pipes, disrupting normal operations.

On construction sites, suspended solids typically originate from soil, silt, clay and cementitious materials. Activities such as excavation, piling, cutting and vehicle movements can significantly increase suspended solids in water.

Dissolved In-Organic Chemicals

Components such as calcium, sulphate, cyanide or toxic metals can be found in trade effluent. These substances can damage sewer infrastructure or affect downstream treatment processes.

In construction, these chemicals may arise from ground conditions, contaminated land, or materials used during the build process.

High pH

Water will develop a high pH through contact with cementitious products on site and is a common issue. A maximum and minimum limit will be applied in your licence as this can adversely impact wastewater treatment processes.

Concrete pours, washout areas and grouting operations are typical sources of high pH water on construction sites.

Other

Depending on the type of activities being carried out, various other components can be present. Whilst present in small concentrations, they can be highly toxic or resistant to treatment.

These may include hydrocarbons from machinery, cleaning agents from site welfare facilities, or additives used in construction processes.

Treatment for Main Pollutants

Treatment is required to ensure that trade effluent meets the conditions specified in the licence before discharge.

pH

Managing acidic and alkaline pH requires different approaches. For acidic water, alkali such as sodium hydroxide or lime can be added. For alkaline water, acids such as hydrochloric or sulphuric acid, or carbon dioxide, can be used.

On construction sites, this is particularly relevant for concrete-related activities where water often becomes highly alkaline.

Suspended Solids

Settlement tanks and lamella clarifiers are commonly used to recover medium and coarse particles. These systems allow solids to settle out before discharge.

This is especially important during early construction phases where ground disturbance is high.

Biochemical Oxygen Demand (BOD)

BOD may be present as suspended or dissolved matter. When dissolved, it is typically treated through biological or chemical oxidation.

Chemical Oxygen Demand (COD)

COD covers a broader range of substances, including those resistant to biological breakdown. Treatment approaches are similar to BOD but may require additional processes depending on the contaminants.

Metals

Metals may exist in particulate or dissolved form. Larger particles can be removed through sedimentation, while dissolved metals often require chemical treatment processes.

Fats, Oils, Greases

These are typically removed using oil-water separators. On construction sites, they may originate from plant machinery or maintenance activities.

Why Treatment is Important

As stated under Section 118 of the Water Industry Act 1991, discharging trade effluent without consent is an offence and can lead to fines and prosecution.

Discharging without consent can lead to:

• Damaging the sewers
• Disrupting sewage works
• Harm to the environment
• Health risks for workers and the public

If non-compliance continues, the sewerage company can prevent further discharge into their systems, which can have a direct impact on construction progress.

Environmental regulators in the UK include the Environment Agency, NRW, SEPA, local water boards and local councils.

Following the 2025 IWC report, changes to regulatory frameworks may be introduced, meaning contractors should remain aware of evolving requirements. You can read our summary on these changes and what it means for the water industry here >

Conclusion

Managing trade effluent on construction sites is a critical element of both environmental compliance and operational efficiency. From understanding what constitutes trade effluent, to applying for licences, managing costs and implementing effective treatment, each stage requires careful planning and control.

Construction activities generate a wide range of water-related challenges, but with the correct processes and equipment in place, these can be effectively managed.

By taking a proactive approach to trade effluent management, contractors can reduce risk, avoid delays and ensure compliance with regulatory requirements, while also maintaining safe and efficient site operations.