Constructed wetlands for water treatment



Constructed wetlands make use of the natural purification processes of vegetation, soils and microbes to remove contaminants from discharge. Uses of constructed wetlands for water purification include applications in industrial wastewater and municipal wastewater and storm water treatment. This relatively low-cost technology improves water security and access, making it important for climate change adaptation. Additionally, green spaces created by wetlands produce habitats for wildlife and may improve recreational value. There are two main types of constructed wetlands: subsurface flow and surface flow. Both are constructed on top of an impermeable basin that is placed in the ground. Subsurface flow wetlands filter and purify water under the surface of the soil, and are therefore filled with porous soils and sand. Water is either purified vertically through the soil and collected in pipes in the underlying basin, or goes through the soil layer in a more diagonal direction due to a slant, after which it is also collected in pipes and sent to an external reservoir. Surface flow wetlands consist of more impervious, silty soils that keep water above the soil. The water moves slowly in a horizontal pattern through the vegetation and top soil, removing sediment and contaminants before it is collected in pipes at the wetland’s end.

Needs Addressed

Altered water use techniques


Site selection typically includes a low-lying area so that discharge can be easily collected for example, next to a road, near municipal water-storage tanks, or similar locations. Key variables to consider include required land size, expected (and desired) water retention capacity and water retention time, based on site capacity and purification needs. Construction activities typically include placing underlying basin at the site, topping the basin with soil (tailored to the respective requirements of surface and subsurface wetlands), and planting vegetation. Preference is usually given to native species, which can tolerate high moisture and which have good ability to retain contaminants. Monitoring and maintenance of the wetland includes removal of invasive species, clearing clogs, and monitoring water flow and water quality (pollution removal efficiency).

Adaptation Effects

  • Ecologically sustainable method of wastewater treatment to enhance water security in the face of restricted access usable water sources
  • Constructed wetlands do not allow mosquitoes to breed and therefore limit the increase in waterborne diseases resulting from climate change

Overview and Features

Employs wetland vegetation to provide a controlled environment in which to treat wastewater. Constructed wetlands can be used to treat urban and industrial wastewater, though not sewage water. They include either Free Water Service systems, in which water flows above the ground with vegetation planted in the water bed, or Subsurface Flow systems, in which water flows through a porous material which has vegetation planted within it.


  • Relatively low costs for construction and operation
  • Gravel and other resources for construction and site preparation processes can be very costly

Energy Source

Human resources for construction

Ease of Maintenance

  • Low maintenance demands
  • Maintenance tasks include removal of litter, replacing plants and removing weeds, controlling water flow etc.

Technology Performance

  • Inappropriate design processes in the past have hindered success in implementation and sustainability
  • Constructed wetlands are able to manage changes in water levels and contamination densities
  • Processing rates depend on environmental factors such as temperature, oxygen and pH, and water volume capacity

Considerations (technology transfer criteria, challenges, etc.)

  • Comprehensive design processes require an interdisciplinary team of experts in chemistry, hydrology, soil science, plant biology, natural resources, environmental management, ecology, environmental engineering, surveying, and project management.
  • The design and planning process must incorporate an understanding of the complex physical, biological and chemical aspects of the technology
  • Requires the technical knowhow to plan, design and implement alongside knowledge of the most recent developments in the technology
  • The design and operation of constructed wetlands must be adjusted according to the context of its implementation, accounting for differing climates and contextual priorities e.g. nutrient removal versus removal of pathogenic organisms
  • Some wastewater may need to be pre-treated before applied to constructed wetlands in order to enable to appropriate functioning of the biological elements of the wetlands
  • A lack of understanding of the complexity of ecological systems can hamper the effectiveness of constructed wetlands

Co-benefits, Suitability for Developing Countries

  • Provide green space, wildlife habitats and recreational and educational areas
  • Constructed wetlands are a low-maintenance, ecologically sustainable, simple, robust, low cost and low energy technology thereby providing a feasible technology option in developing countries
  • Land tenure issues can provide a barrier as the wetlands require large spaces in which to operate
  • Operate at community level and are therefore located close to communities
  • Provides water purification and biological control and improves water quality.
  • Provides water regulation in extreme conditions, such as during floods and droughts.
  • Provides aesthetic, educational and recreational value for local populations.
  • Reduces water treatment costs.
  •  Improves climate change adaptation to extreme conditions.



  • Construction and operation is often much cheaper than conventional treatment plants, lowering energy costs
  • Lowers investments in treatment infrastructure
  • Often operated at the community level – decentralized solution
  • Produces multiple benefits, including climate change adaptation and biodiversity benefits (achieves multiple targets and has multipurpose applications)
  • Subsurface wetland systems filter water without attracting mosquitos that transmit malaria and other vector borne diseases


  • Wetlands require relatively large areas, which can make it difficult and expensive to gain land tenancy rights
  • Wastewater containing high volumes of contaminants, particularly metals, can have negative effects on plants and animals and may not be suited for wetland treatment t
  • Surface wetland systems could provide habitats for mosquitos, increasing risk of vector-borne diseases
  • Unexpected disease or invasive species may disrupt habitat functions

Implementation considerations*

Technological maturity: 3-5
Initial investment: 2-3
Operational costs: 1-2
Implementation timeframe: 2-3

* This adaptation technology brief includes a general assessment of four dimensions relating to implementation of the technology. It represents an indicative assessment scale of 1-5 as follows:

Technological maturity: 1 - in early stages of research and development, to 5 – fully mature and widely used
Initial investment: 1 – very low cost, to 5 – very high cost investment needed to implement technology
Operational costs: 1 – very low/no cost, to 5 – very high costs of operation and maintenance
Implementation timeframe: 1 – very quick to implement and reach desired capacity, to 5 – significant time investments needed to establish and/or reach full capacity

This assessment is to be used as an indication only and is to be seen as relative to the other technologies included in this guide.
More specific costs and timelines are to be identified as relevant for the specific technology and geography.


  • Rehabilitation of Wetland Cell and Replanting of Wetland Plant at Tasik NAHRIM, Malaysia
  • Wai Bulabula Wetlands Treatment Systems in Fiji

Information Resources

  • UNEP-DHI Partnership- Constructed wetlands for water treatment
  • Kayombo, S., Mbwette, T.S.A., Katima, J.H.Y., Ladegaard, N. and Jørgensen, S.E. n.d. Waste Stabilization Ponds and Constructed Wetlands Design Manual. UNEP-IETC and Danish International Development Agency (Danida). Available from: [[1]] [18 January 2015]
  • Vymazal, J and Kröpfelová, L. 2008. Wastewater Treatment in Constructed Wetlands with Horizontal Sub-Surface Flow. Springer Science and Business Media B.V.