Indicator Assessment

Emission intensity of the domestic sector in Europe

Indicator Assessment
Prod-ID: IND-360-en
  Also known as: WREI 002
Last modified 11 May 2021
14 min read

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This page was archived on 10 Feb 2021 with reason: Other (Discontinued indicator)

The absolute decoupling of nutrient emissions from the domestic sector and population growth, over a period of almost two decades (1990-2011), is observed in fourteen countries (Austria, Belgium, Czech Republic, Germany, Denmark, Greece, Finland, Ireland, Malta, the Netherlands, Norway, Portugal, Slovenia and Turkey). The actual extent of decoupling, and the differences in trends among countries, may be partially explained by the different numbers of inhabitants connected to tertiary wastewater treatment technologies.

When making an EU wide comparison of the extent of decoupling of nutrient emissions from population growth, the actual proportion of the population connected to different types of wastewater treatment (elaborated in indicator CSI 024) and the completeness of data available on the population connected to collecting systems without treatment should be taken into consideration. The implementation status of the Urban Waste Water treatment Directive (UWWTD), which protects the water environment from the adverse effects of discharges of urban waste water, as well as the level of investment in water and wastewater management, may have an impact. Similarly, the implementation status of the Water Framework Directive (WFD) and Groundwater Directive may also have an impact. Furthermore household patterns and household income level affect the production and composition of wastewater and should also be considered.

It is assumed that the use of actual data on loads discharged from wastewater treatment plants, combined with the load values calculated for the population not connected to wastewater treatment, would add value to the decoupling indicator as it would better reflect the real situation.


Decoupling of nutrient emissions from urban wastewater discharge and population growth

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Nitrogen emission intensity of the domestic sector

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Phosphorus emission intensity of the domestic sector

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The most significant decoupling of domestic nutrients emissions in water and population growth was recorded in Malta and Greece, where both nitrogen and phosphorus emissions decreased by more than 60%, whereas the population grew by 7% and 16% respectively. Despite population growth over the last two decades, a significant reduction in domestic nutrients emissions in water also occurred in Austria and Netherlands, where there was a nearly 50% reduction in nitrogen emission, and a more than 60% reduction in the phosphorus emission load. Population growth in the Czech Republic and Germany was 2.3% and 3.4% respectively. This was not as high as in the Member States mentioned above although the reduction of nutrient loads discharged from the domestic sector was also considerable in these countries, with, respectively, about a 42% and 34% reduction in the nitrogen emission load, and a reduction in phosphorus emission of about 61%. In Austria, Denmark, Finland, Germany, Greece, the Netherlands and Sweden, at least four out of every five individuals are connected to wastewater treatment plants equipped with tertiary treatment facilities. A decrease in emissions coupled with a decrease in population growth occurred in Estonia, Bulgaria, Hungary and Romania, however, the rate of emission decrease was greater than the rate of population decrease.

A decrease of nutrient emissions was observed in 18 of the 22 states assessed. A slight increase of nutrient emissions in Poland, where population growth over the last decade was insignificant, may be attributed to data quality rather than increased pollution generation. Values of nitrogen emission intensity for 2011 range from 1.21  to 3.82 kg of total nitrogen per inhabitant per year. The 2011 values for total phosphorus range from 0.19 to 0.84 kg per inhabitant per year. Between 1990 and 2011, nitrogen and phosphorus emission intensity decreased by more than 50% in Austria, Malta, Greece and the Netherlands. These countries reported a relatively high percentage of the national population connected to wastewater treatment and a low percentage of the population connected to collecting systems without treatment or with no treatment. For some countries, such as Switzerland, Finland and Sweden, where relatively small changes in decoupling over the two decades are observed, emission intensities for nitrogen and phosphorus were already relatively low from the early 1990s.

Current emission intensity calculations, which are based on default treatment efficiencies per treatment type, mostly reflect the status of wastewater infrastructure in Europe, but do not make it possible to differentiate between countries that apply more advanced (and more efficient) treatment technologies, and countries that implement the minimum requirements of the UWWTD. More precise data is presented in the 2012 values of emission intensity for Austria, Czech Republic, Germany, Denmark, Lithuania, Luxembourg, the Netherlands and Slovenia in the last vertical bar in Figs. 2 and 3, respectively (based on emission data reported under the UWWTD). Nitrogen emission intensity values, calculated on the basis of default p.e. values, are on average 20% higher than the values derived from actual reported nitrogen emissions. In the case of phosphorus, the differences are even higher, the calculated emission intensity values are about 30% higher than the values derived from reported emission data. This shows that several UWWTPs perform better than the default values, and also, very likely, better than UWWTD legal requirements. As such, optimising performance and providing  data on actual emissions may further underpin this more positive picture of the real situation and developments in wastewater treatment in Europe.

Supporting information

Indicator definition

This indicator is used to illustrate the emission intensity of the domestic sector (household plus services), expressed as the amount of discharged pollutant from wastewater treatment/or discharged without treatment per inhabitant per year. Furthermore, the indicator shows a decoupling of the emission of nutrients (nitrogen and phosphorus) and population growth across Europe.

The values of change (increase/or decrease) in discharged load between 1990 and 2009 (expressed in percentages, where values in 1990 = 100%) are plotted against the values of change in population growth.

Absolute decoupling occurs when the environmentally relevant variable is stable or decreasing while the driving force is growing. Relative decoupling occurs when the growth rate of the emission is positive, but less than the population growth rate.


Emission intensity is expressed in kilogrammes of pollutant per inhabitant per year. Changes in pollutant emissions from households between 1990 and 2009 are expressed in percent, where the values recorded in 1990 represent 100%. Changes in population between 1990 and 2009 are expressed in percent, where the values recorded in 1990 represent 100%.


Policy context and targets

Context description

In March 2010, the European Commission issued ‘Europe 2020 strategy’ - the European Strategy for smart, sustainable and inclusive growth. It highlights – among other things - the need for a more resource efficient economy. The “Flagship initiative” under the Europe 2020 strategy, called “A resource efficient Europe”, establishes resource efficiency as the guiding principle for EU policies on energy, transport, climate change, industry, commodities, agriculture, fisheries, biodiversity and regional development.   The Roadmap to a Resource Efficient Europe defines medium- and long-term objectives to achieve efficient resource use in the region. Decoupling, in the sense of breaking the link between economic growth and resource use, is a central concept of the strategy for making Europe resource efficient. The 2050 vision and the objectives for 2020 are to be addressed in the sector initiatives that shall contribute to the resource-efficient Europe Flagship Initiative (i.e. the 7th EU Environmental Action Programme or the revision of the Common Agriculture Policy, Water Framework Directive and Groundwater Directive).


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 discharge and 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 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 population equivalent that discharge into fresh waters, while more advanced treatment (tertiary treatment) is required for discharges into sensitive areas.

The achievements through the UWWTD have to be seen as an integrated part of objectives under the Water Framework Directive (WFD), which aim at a good ecological and chemical status for all waters by 2015. That means that more stringent emission targets may be set in case it is needed for achieving the good status.

EU wide targets related to the nutrient emission intensity of domestic sectors, or the decoupling of nutrient emission from population growth have not been set.

Related policy documents

  • European Waters – Assessment of Status and Presures
    This report's results present good and robust European overviews of the data reported by the first RBMPs, and of the ecological status and pressures affecting Europe's waters. Europe's waters are affected by several pressures, including water pollution, water scarcity and floods. Major modifications to water bodies also affect morphology and water flow. To maintain and improve the essential functions of our water ecosystems, we need to manage them well.
  • Roadmap to a Resource Efficient Europe COM(2011) 571
    Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions. Roadmap to a Resource Efficient Europe.  COM(2011) 571  
  • Urban Waste Water Treatment Directive
    Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment The Urban Waste Water Treatment Directive (UWWTD) aims to protect the environment from the adverse effects of urban wastewater discharges.


Methodology for indicator calculation

For overall emission load the following formula was used:

Ntotdischarged= Ntot(coll.system)+Ntot(without treatment)+ Ntot(IAS)+Ntot (primary)+ Ntot(secondary)+ Ntot(tertiary)


Where  Ntotdischarged  is a total annual nitrogen load discharged from collecting systems or wastewater treatment plants [kg/y]


Ntot(coll.system) is a total annual nitrogen load discharged from collecting systems without treatment [kg/y]


Ntot (primary) is a total annual nitrogen load discharged from wastewater treatment plants with primary treatment [kg/y]


Ntot(secondary) is a total annual nitrogen load discharged from wastewater treatment plants with secondary treatment [kg/y]


Ntot(tertiary) is a total annual nitrogen load discharged from wastewater treatment plants with tertiary treatment (N, P removal)  [kg/y]


For calculation of the Ntot(coll.system) and Ntot(without treatment) the population equivalent for nitrogen and phosphorus was used. For calculation of the Ntot(IAS), removal efficiencies, corresponding to the primary treatment were applied.


Two approaches were used to calculate nutrient discharged loads (Ntotdischarged and Ptotdischarged) of the domestic sector:

  • The "default” approach is based on the percent values of the population connected to different types of waste water treatment (Based on Eurostat Water Statistics), and the default values of nutrient population equivalent and removal efficiency per type of treatment (primary, secondary, and tertiary).

p.e. for Nitrogen= 12 g/d

p.e. for Phosphorus=2,5 g/d

Removal efficiency :

Nitrogen (primary)=0,15

Nitrogen (secondary)=0,35

Nitrogen (tertiary)=0,70

Phosphorus (primary)=0,10

Phosphorus (secondary)=0,20

Phosphorus (tertiary)=0,80

  • A second approach was used to illustrate the actual emissions from urban treatment plants based on data reported voluntarily by 13 Member States (BE, CY, CZ, DE, DK, EE, ES, IT, LT, LU, LV, NO,  SI) under the UWWTD (2011 data request). Complete datasets on the emission load discharged from treatment plants (size ≥2000 p.e) were available for AT, NL, CZ, DE, DK, LT, LU and SI.

For these eight countries, the total discharged load was calculated according to the following formula:

Ntotdischarged= Ntot(WWTPs) + Ntot(coll.system)+Ntot(without treatment)+ Ntot(IAS)

Where Ntot(WWTPs) corresponds to the sum of discharged loads reported under the UWWTD for individual treatment plants normalised by overall entering load in population equivalent (to make adjustment for industrial share in the load entering into urban waste water treatment plants) and finally multiplied by the total population connected to UWWTPs. 

Calculation of Ntot(coll.system), Ntot(without treatment) and  Ntot(IAS) is explained above.

For the remaining five Member States, the gap analysis was done. Where gaps (missing data on discharged load) did not exceed 30% of the total entering load (EE, NO), data gap filling was done, with emission load values calculated (for each type of treatment) from the formulae specified below. The formulae were derived from the 13 Member State emission load datasets (for UWWTPs > 2000 p.e.) .

The formulae used for calculation of the Ntot  and Ptot (primary), Ntot and Ptot (secondary), Ntot  and Ptot (tertiary) express the annual nutrient load discharged as a function of the reported entering load the treatment plant, (L) [p.e].

The units for the emission factors listed below are kg/y per population equivalent entering load and the emissions include the proportions from households, services as well as connected industry.

Ntot(primary)= 0,004*L


Ntot(tertiary)=0,0014*L, for tertiary treatment with N removal

Ntot(tertiary)=0,0009*L+9,43318, for tertiary treatment with P removal

Ntot(tertiary)=0,0008*L , for tertiary treatment with N and P removal


A similar approach was applied to the calculation of the total phosphorus discharged load.

Ptot (primary)= 0,00009*L


Ptot(tertiary)= 0,0001*L+1,1658, for tertiary treatment with N removal

Ptot(tertiary)=0,0001*L, for tertiary treatment with P removal

Ptot(tertiary)=0,00005*L+0,4182, for tertiary treatment with N and P removal


Methodology for gap filling

See the alternative approach (above) based on formulae derived from available emission load data in the UWWTD Waterbase .


Methodology references

No methodology references available.



Methodology uncertainty

  • The nutrient population equivalent may vary among European states and over the stated time period. This variation is not included in the pollution load generation based on Eurostat data. Nutrient removal efficiency is more likely higher, in some countries, than the default values used for the calculation and may also have developed over the time period for the same treatment types.
  • Use of actual emissions reported under the UWWTD would be more suitable for the indicator (as documented by additional assessment). However, the load data reported under the UWWTD is not available for all Member States, nor for the required temporal coverage (i.e. 1990s - dataset incomplete).
  • Effluent from the UWWTPs may also include different shares of loads attributed to services and industries, which affect emission intensity values. This impact on the indicator could be further reduced if the industrial load proportion for the relevant parameters could be excluded before normalising per inhabitant connected to the UWWTP.

Data sets uncertainty

  • An older version of Eurostat JQ was used for the assessment (population connected to wastewater collection and treatment systems, [env_watq4] version June 26, 2013), as it included data covering the period from 1990s to 2010s. The dataset on population connected to wastewater collection and treatment systems, which is currently available in Eurostat, contains data covering the period from the 2000s. The indicator will be updated once the dataset in Eurostat covers the entire period analysed.
  • Based on comparative analysis between data reported under SoE Emissions (, ) for seven countries (EE, LT, LV, NL, RO, SE and SI) and emissions reported under the UWWTD, differences were typically 20-25%, however, major inconsistencies for P-emissions were observed for NL and SI.


Rationale uncertainty

No uncertainty has been specified

Data sources

Other info

DPSIR: Pressure
Typology: Efficiency indicator (Type C - Are we improving?)
Indicator codes
  • WREI 002
Frequency of updates
Updates are scheduled every 2 years
EEA Contact Info


Geographic coverage

Temporal coverage