Indicator Assessment

Urban waste water treatment - outlook EEA

Indicator Assessment
Prod-ID: IND-76-en
  Also known as: Outlook 047
Published 08 Jun 2007 Last modified 11 May 2021
13 min read
This page was archived on 12 Nov 2013 with reason: Content not regularly updated

Assessment is created in 2007

By increasing the connection rate of the European population and the use of tertiary treatment, implementation of the UWWT directive is expected to make it possible to increase the amount of wastewater treated while reducing total discharges of nutrients.

The diverse situation in European countries regarding wastewater treatment systems is a challenge to the implementation of EU directives.

Diffuse sources of nutrients (e.g. agriculture) are expected to become prime issues to address as implementation of directives targeted at point sources results in significant reductions in their environmental impact (e.g. eutrophication).

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Discharges of nitrogen and phosphorous from wastewater treatment plants

Note: N/A

Data source:

EEA European Topic Centre on Water: National Environmental Research Institute + International Office for Water + WRc, 2003-2004. Dataset: ETC/WTR model.

Industrial production and household consumption increased at a rapid rate during the last century, producing larger amounts of wastewater. The extent to which this is discharged into surface waters depends on the sewage collection and treatment facilities available, as well as on the content of the items produced or consumed (e.g. phosphorus in detergents). In Europe most phosphorus loading of surface waters is attributable to discharges from point sources (in particular municipal sewage and industrial effluents), while nitrogen loading comes mainly from the use of nitrogen fertilisers and manure in agriculture.

The central piece of legislation for this outlook is the Urban Waste Water Treatment Directive (91/271/EEC) (148). It is a key EU water policy, which aims at protecting the environment from the adverse effects of urban wastewater discharges. The directive sets minimum standards for the collection, treatment and disposal of wastewater that depend on the size of the agglomeration, and the type and sensitivity of the receiving waters. In general terms, the directive has to be fully implemented in the EU-15 countries by the end of 2005 and in the New-10 in the 2008-2015 period; the majority of the urban population will then be connected to tertiary or secondary treatment.

Current and projected levels of wastewater treatment in Europe

Note: Current and projected levels of wastewater treatment in Europe

Data source:

EEA European Topic Centre on Water: National Environmental Research Institute + International Office for Water + WRc, 2003-2004. Dataset: ETC/WTR model.

Since many EU-15 countries have delayed implementing the UWWT directive, and the New-10 have diverse transition periods, this outlook reports the expected discharges of nutrients after the implementation of the directive rather than by a specific date. There are many requirements and deadlines for implementation of the directive, and there is significant uncertainty regarding its final implementation.

Implementation of the UWWT directive is expected to lead to the following developments (see Figures 1 and 2) (149):

  • A dramatic shift towards tertiary treatment is expected in the New-5 (Estonia, Czech Republic, Poland, Hungary and Slovenia) and Belgium and Luxembourg (Group 2), at the expense of primary and secondary treatment and significant levels of discharge without treatment. In the New-5, these improvements are expected to be accompanied by an increase in the connection of the population to wastewater treatment plants from 57 % to 70 %. For the Group 3 countries and the United Kingdom, in all of which a relatively low proportion of the territory is designated as sensitive area, the future development of wastewater treatment is expected to be characterised by an increasing connection rate (from 67 % to 80 %) and an enhanced diffusion of secondary treatment. Finally, only minor changes in the level and type of wastewater treatment are expected in Group 1 countries, since they already almost (i.e. in terms of level and type of wastewater treatment) and have a very limited amount treated only in primary facilities or discharged without treatment.
  • Considerable reductions in nutrient discharges are expected in countries that experience a dramatic increase in tertiary treatment. Belgium and Luxembourg are projected to reduce their total discharges of nitrogen and phosphorous by 40 % and 80 % respectively. In the New-5, discharges are projected to decrease from 3 to 2.3 kg N/person/year (a 24 % reduction), and 0.4 to 0.15 kg P (62 %). In contrast, total discharges in Group 3 countries are expected to increase since the percentage of the population connected to UWWT plants will increase significantly while tertiary treatment will remain limited: nitrogen and phosphorous discharges are projected to increase by about 14 %, which, compared with a 29 % increase in the connected population, leads to a slight decrease of nutrient discharges per capita. Finally, discharges are expected to remain nearly unchanged in countries that have already almost achieved the directive's requirements (Group 1).
  • Overall nitrogen and phosphorus discharges in countries with high levels of tertiary treatment are expected to be about 2.3 kg N/person/yr and 0.1 kg P. Countries that plan to rely essentially on secondary treatment are expected to have significantly higher discharges, in particular for phosphorous, by an estimated factor of three.
  • At the country level, data and information on wastewater treatment and population distribution in terms of size of agglomeration are limited and heterogeneous, hence very difficult to compile into a European overview. There is also some uncertainty about the detailed national implementation of the UWWTdirective (150). As a consequence, the projections reported here are subject to some uncertainty, and might conflict with national assessments.

By increasing the connection rate of the European population, the UWWT directive would in principle increase discharges of nutrients from UWWT plants; however, the increasing use of tertiary treatment that should result would make it possible to increase the amount of wastewater treated and achieve an overall decrease in discharges of nutrients. The net benefit to the environment, in terms of reduced discharges leading to less eutrophication, is therefore considerable since wastewater is expected to be more systematically treated in future and in a more efficient way (151).

Supporting information

Indicator definition

Definition: Percentage of population connected to primary, secondary and tertiary wastewater treatment plants. The indicator illustrates:
1. current level and future changes in level (accordingly UWWT directive)  of population connected to urban wastewater treatment (primary, secondary and tertiary);
2. current level and future changes (accordingly UWWT directive) of discharges of nitrogen and phosphorous from wastewater treatment plants

Model used: Water Model from EEA/ETC

Ownership: European Environment Agency

Temporal coverage: 2005, 2008-2015 (objectives of the UWWT directives)

Geographical coverage: EU 15 : Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain, Sweden, United Kingdom; EU -5: Estonia, Hungary, Check Republic, Polamd, Slovenia,


1) Percentages of population connected to urban wastewater treatment;

2) Kg of nitrogen and phosphorous per inhabitant per year.


Policy context and targets

Context description

Global and Pan-European policy context

Indirectly the indicator can be useful within UN "Millennium Development Goals" and with the WSSD Plan of Implementation to ensure access to adequate drinking water and sanitation services.

EU policy context

The Urban Wastewater Treatment Directive (UWWT) prescribes the level of treatment required before discharge. It requires Member States to provide all agglomerations of more than 2 000 population equivalents (p.e.) with collecting systems. Secondary treatment (i.e. biological treatment) must be provided for all agglomerations of more than 2 000 p.e. discharging into fresh waters. Special requirements with intermediate deadlines depending on the sensitivity of the receiving waters are placed on agglomerations of more than 10 000 p.e. with various size classes of agglomerations. The performance of the treatment is assessed using 5 different determinands (BOD, COD, TSS, Ntot and Ptot). In the 15 Member States, there are about 20 000 agglomerations with more than 2 000 p.e., the population is 376 million inhabitants and the treatment capacity for the 8 181 agglomerations for which Member States provided detailed data is equivalent to organic matter from 469 million p.e.
For agglomerations smaller than described above and those equipped with a collecting system, the treatment must be appropriate, meaning that the discharge allows the receiving waters to meet the relevant quality objectives.
The WFD is asking for the estimation and identification of significant point and diffuse source pollution, in particular by substances listed in Annex VIII, from urban, industrial, agricultural and other installations and activities, based, inter alia, on information gathered under Articles 15 and 17 of Directive 91/271/EEC and other Directives. From the substances listed in the Annex VIII, the following are important for the indicator: substances which have an unfavourable influence on the oxygen balance (and can be measured using parameters such as BOD, COD, etc.), materials in suspension, and substances which contribute to eutrophication (in particular, nitrates and phosphates). Member States should thus take the necessary steps to build a data collection system able to provide these data, urban source being one of the sources listed. The ultimate aim of this is to reach the target of the WFD that is a good chemical and biological status for all waters in 2015, the discharge of substances being one of the major problems to face.

EECCA policy context

EECCA Environmental Strategy reveals main efforts in the region to improve quality of water and wastewater collcetion through more effective institutional and regulatory framework.


EU level

The Urban Waste Water Treatment Directive (UWWTD; 91/271/EEC) aims to protect the environment from the adverse effects of urban wastewater discharges. It prescribes the level of treatment required before dischargeand has to be fully implemented in the EU-15 countries by 2005 and in the ten new Member States by 2008 - 2015. The directive requires Member States to provide all agglomerations of more than 2 000 population equivalent (p.e.) with collecting systems and all wastewaters collected to be provided with appropriate treatment by 2005. Secondary treatment (i.e. biological treatment) must be provided for all agglomerations of more than 2 000 p.e. that discharge into fresh waters, while more advanced treatment (tertiary treatment) is required for discharges into sensitive areas. To help minimise pollution from various point sources, the Integrated Pollution Prevention and Control directive, which came into force 1996, has a set of common rules on permitting for industrial installations.
The achievements through the UWWTD and the IPPC directive have to be seen as an integrated part of objectives under the Water Framework Directive (WFD) which aim at a good chemical and biological status for all waters by 2015.

EECCA level

  • To increase wastewater collection and treatment in the long term


Links to other policies

UN 'Millenium Development Goals'

EECCA Environmental Strategy

Related policy documents

  • COM(2004) 248 final
    Implementation of Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment, as amended by Commission Directive 98/15/EC of 27 February 1998
  • Urban wastewater treatment summary report
    Summary report on: the identification of sensitive areas by the Member States; the measures implemented by the Member States with the view to the deadline of 31 December 1998; wastewater treatment in major cities; verification of the identification of sensitive areas by the Commission.
  • Water Framework Directive (WFD) 2000/60/EC
    Water Framework Directive (WFD) 2000/60/EC: Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy.


Methodology for indicator calculation

The methodology used consists of a simple techno-economic model developed by EEA European Topic Centre on Water in 2004, which links discharges of nutrients to population growth in areas connected to sewers and to developments in treatment technologies. The model covers most of the EU member countries and intends to reflect the level of nutrient discharges (i.e. nitrogen (N) and phosphorous (P)) after the urban waste water treatment directive (UWWT, 91/271/EEC) is fully implemented. The future waste water treatment in Cyprus and Malta is uncertain.

Calculating future waste water treatment and discharge from waste water treatment plants are based on information on:

Nutrientcapita: nutrient (N and P) load by waste water per capita and year

POP: population;

%POPconnectedWWT: percentage of population connected to sewers, and water has a retention percentage equal to zero.

A simple formula is used for calculations above:

Emissions= Nutrientcapita*POP*%POPconnectedWWT*(1-(%retention/100).

More detailed information can be available here.

Methodology for gap filling

For variables Nutrientcapita  and POP, there are relatively good estimates. Also good data is provided for the development in national populations. However, information in European coverage of waste water treatment (POPconnectedWWT) and the type of waste water treatment from some countries such as France, Latvia, Lithuania, and the Slovak Republic are missing and for some southern European countries there are no data later than 1995 (e.g. Spain and Italy). This data set has been supplemented with additional national information for some countries France (Ifen 2002); Italy (pers. comm. within the model); Ireland (EPA 2002).

Methodology references



Methodology uncertainty

There is a lot of uncertainty about the actual implementation of the UWWT Directive in the individual countries. In the projections an assumption has been made that all agglomerations greater than 10000 p.e. discharging into sensitive areas will have tertiary treatment and other agglomerations greater than 2000 p.e. will have at least secondary. The category at least secondary treatment cannot be handled in quantitative projections so at least secondary treatment was set to secondary treatment. Coutnries may decide to have better treatment than required by the Directive. For countries with already high waste water treatment the future WWT was set to the current level of WWT, however, information in national and regional SoE reports indicate that they are still upgrading there WWT plants

There is an acknowledged important risk that the simplified calculations of future waste water treatment presented in the methodology might be in conflict with the more detailed national assessment.

Data sets uncertainty

First the current data and information on waste water treatment and population living in different sizes of agglomerations are limited. This makes it necessary to make assumptions with limited information available.

Secondly the information on the current level of waste water treatment is for some countries uncertain and inconsistent. The missing and uncertain data markedly reduce the number of countries for which the waste water treatment before and after can be compared with a sufficient confidence.

Rationale uncertainty

Data sources

  • No datasets have been specified.

Other info

DPSIR: Response
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • Outlook 047
EEA Contact Info


Geographic coverage

Temporal coverage


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