Stormwater treatment

Treating stormwater pollution prevents damage to the environment and protects businesses from the risk of legal and financial penalties.

What is stormwater?

Stormwater is water generated by precipitation—either rainfall or melting snow and ice.

It may infiltrate into the ground, evaporate or flow across impermeable surfaces. This surface runoff is sometimes referred to specifically as surface water.

What pollutants are in stormwater?

Any rain, snow and ice melt that does not infiltrate or evaporate is exposed to pollution present on the ground, and surface water runoff may dissolve or pick up and carry these pollutants and contaminants.

Rainfall on industrial facilities is particularly pone to carrying harmful pollutants, but impermeable surfaces such as roads and pavements make any urban or built environment a potential source of pollution.

The kinds of pollution that may be present in stormwater include:

  • Trash, debris and gross solids
  • Particulate solids—silt, sand, grit and sediment*
  • Nutrients and organic materials
  • Chemicals
  • Heavy metals
  • Oils and hydrocarbons

*Often referred to as TSS, or Total Suspended Solids

Why is stormwater pollution a problem?

Stormwater runoff will eventually reach a watercourse such as a river, lake or sea, and any pollutants that are present in this surface water are deposited into the environment.

Sand, grit and other solids—either carried from impermeable surfaces or as the result of erosion—result in sedimentation and silting of watercourses. Nutrients and organic materials disrupt ecosystems and can cause harmful biological events such as algal blooms. Chemicals, metals and other contaminants may cause direct harm to flora and fauna and may bioaccumulate over time.

For businesses and public bodies alike, permits and discharge limits place stringent regulations on what may be discharged from a site in stormwater. Exceeding these regulatory boundaries can mean that the damage of discharging polluted stormwater is not restricted only to the environment: companies and individuals may also face financial and legal penalties.

What is stormwater treatment?

Stormwater treatment is the action of capturing pollutants and contaminants from surface water runoff before they reach a watercourse or body of water such as a river, lake or ocean.

Once in the environment pollution is difficult to remove, so prevention is always better than cure.

How do you treat stormwater?

Stormwater regulators, engineers and contractors have an enormous responsibility to approve, specify and install treatment solutions that improve water quality and the environment, both today and for years to come.

Fortunately, in the same way that there different kinds of stormwater pollution, there are different techniques, technologies and treatment systems for removing pollutants from surface water.


Stormwater screens are physical barriers that prevent trash, litter, gross solids and larger particles from passing into a drainage network, and may be combined with a form of settling chamber to allow grit and coarse sediment to settle out. 


Hydrodynamic separators use a vortex to remove solids from surface water runoff. This kind of stormwater treatment system settles out grit, sand and silt, capturing along with it any nutrients, chemicals or heavy metals that are bound to the solids.

Depending on the design it may also trap trash and debris, and allow for the separation and capture of oils and hydrocarbons.


A stormwater filter uses filtration media or membranes to remove pollution from surface water. Water is forced through the filter, and the media or membrane captures the pollutants that it was designed to address.

Engineers may tailor media and membranes to capture specific pollutants in order to meet a particular site’s needs. Industrial facilities may need to capture metals such as zinc, lead, copper and aluminium, for example.

Silt, solids, trash and debris are too large to pass through the filter and are typically captured ahead of the filtration unit.


An infiltration system attempts to mimic the natural effect of the soil, providing a permeable surface that stormwater can soak through, often using engineered soils to capture specific pollutants.

The system may also incorporate appropriate biological elements such as plants, both to beautify the area and to intercept nutrients from the water as part of the treatment.


Retention involves the storage of stormwater runoff, both in order to reduce the risk of flooding but also to provide time for pollutants to settle out of the flow.

Landscaping with plants such as grasses, shrubs and wetland flora provides an aesthetically pleasant environment and increases nutrient uptake from the water.

How do you maintain a stormwater treatment system?

All stormwater treatment systems require maintenance in order to operate at the level at which they were designed, and if maintenance is not conducted appropriately, pollution will pass through the system and will damage the environment.

Natural features such as ponds and swales need regular maintenance in order to maintain inward and outward flows, manage plant life and reduce silting. Other treatment systems, such as separators and filters, need regular attention to remove captured pollutants and replace media bags.

Our experience in the US suggests that up to 95% of installed stormwater BMPs (best management practice) are not regularly maintained.

Stormwater treatment solutions

No two stormwater projects are ever the same, so you need to have confidence in your system and the company backing it.

We have decades of experience of designing, installing and maintaining stormwater treatment systems. Our systems and expertise can help you to protect the environment and reduce the risk of the financial and legal penalties associated with stormwater discharge pollution.

Work with us to:

  • Size, scale and specify the right solution
  • Get expertly designed solutions that fit your specification and your budget
  • Be confident that your system will meet site-specific regulations for stormwater treatment

Contact us to find your nearest representative. 

Learn more about our stormwater treatment solutions

Downstream Defender®

Downstream Defender® is an advanced hydrodynamic vortex separator that provides impressive and reliable removals of sediments, oil and floatables from stormwater runoff.

First Defense®

First Defense® is a versatile stormwater separator that works with single and multiple inlet pipes and inlet grates. 

Up-Flo® Filter

The Up-Flo® Filter is an advanced stormwater treatment solution that combines sedimentation and screening with fluidised bed filtration to deliver exceptional surface water pollution removal.


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