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Where does our wastewater go?

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Water is a renewable resource that is provided naturally and delivered to our taps by a complex network of pipes, pumps and equipment. After using it in our homes and businesses (i.e. after you’ve flushed the toilet, done the dishes, or had a shower), it usually contains various pollutants, depending on what it was used for, and therefore, which may affect the quality of fresh and marine water and present a risk to human health and biodiversity. This used water is called wastewater.

In order to minimize the adverse effect to the environment, the wastewater journey begins once water goes down the drain. Most homes in urban areas are connected to a sewerage system that carries wastewater to a treatment plant. Once the sewage has been cleaned up to the desired level (now termed “treated effluent”), the effluent is reused or discharged back into the environment.

Waste Water Treatment – EPA (source)

In the EU, the Urban Wastewater Treatment Directive (UWWTD; Council Directive 91/271/EEC) establishes minimum requirements for collection, treatment and discharge of urban wastewater. The Directive specifically requires all European agglomerations[1] with a size of more than 2,000 population equivalents (p.e.)[2] be equipped with collecting and treatment systems for their waste waters. It also provides for biological wastewater treatment (secondary treatment[3]) to significantly reduce the biodegradable pollution in wastewater. In addition, before the wastewater is discharged in the sensitive areas[4] and their related catchments, more stringent treatment is required to eliminate nutrients (mainly nitrogen and/or phosphorus).

The Directive imposes different reporting obligations. Data reported by Member States in relation to Article 15 of the Directive, which stipulates that discharges from urban waste water treatment and amounts and composition of sludges disposed to surface waters must be monitored to verify the compliance with specific provisions of the Directive, are included in the Waterbase-UWWTD. Available data on urban wastewater treatment plants (UWWTPs) and discharge points have been considered to create two new geodatabases for the EMODnet Human Activities portal. They are based on the data corresponding to year 2014.

The dataset on UWWTP presents the available information (localization, capacity and actual load treated, type of treatment, aggregated data on the performance of plants) on individual UWWTP and collecting systems without UWWTP located in coastal NUTS3 regions, those that limit with transitional and/or coastal water bodies (as defined in the Water Framework Directive).

On the other hand, the dataset on discharge points presents the available information (localization of discharge, link to specific treatment plant, type of receiving area into which the effluent/wastewater is discharged, related waterbody/river basin) on individual points of discharge from treatment plants or collecting systems located in coastal NUTS3 regions.

Detailed information about the UWWTD and its implementation is available from the European Commission website. More up-to-date information may be available from national water/waste water websites.

Waste Water Map


[1] The UWWTD defines an agglomeration as an area where the population and/or economic activities are sufficiently concentrated for urban wastewater to be collected and conducted to an urban wastewater treatment plant or to a final discharge point.

[2] The size of an agglomeration in terms of generated pollution load is measured in “population equivalent” (p.e.). This is the organic biodegradable load that has a five-day biochemical oxygen demand (BOD5) of 60 g of oxygen per day, or in more popular terms – the organic biodegradable load generated by one person per day.

[3] Treatment of urban wastewater by a process generally involving biological treatment with a secondary settlement or other process in which the requirements established in Table 1 of Annex I of the UWWTD are respected.

[4] Sensitive areas: freshwater bodies, estuaries and coastal waters which are eutrophic or which may become eutrophic if protective action is not taken; surface freshwaters intended for the abstraction of drinking water which contain or are likely to contain more than 50 mg/l of nitrates; and areas where further treatment is necessary to comply with other Council Directives such as the Directives on fish waters, on bathing waters, on shellfish waters, on the conservation of wild birds and natural habitats, etc.

The information and views set out in this blog are those of the author and do not necessarily reflect the official opinion of the European Commission. Neither the European Commission nor any person acting on the European Commission's behalf may be held responsible for the use which may be made of the information therein.

September 19th, 2019 | Written by

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