Absolute decoupling of nutrient emissions from domestic sector and the population growth over the period of almost two decades (1990-2009) is observed in thirteen countries (Austria, Belgium, Czech Republic, Germany, Greece, Finland, Ireland, Switzerland, the Netherlands, Norway, Portugal, Slovenia and Turkey). The actual extent of decoupling, and the differences in trends among countries, may be partially explained by different levels of numbers of inhabitants connected to tertiary wastewater treatment technologies
When making the EU wide comparison of the extend of decoupling of nutrient emissions from population growth, the actual rate of population connected to different types of treatment (elaborated in the CSI 024) should be taken into consideration, and completeness of the data available on population connected to collecting systems without treatment. The status of the implementation of the UWWTD which protects the water environment from the adverse effects of discharges of urban waste water, the level of investment in the water and wastewater management ,as well as the status of the implementation of the Water Framework Directive (WFD) and Groundwater Directive may have an impact. Furthermore household patterns as well as the household income level affecting the production and composition of waste water should be considered as well.
It is assumed that the use of actual data on loads discharged from wastewater treatment plants combined with the load values calculated for population not connected to the waste water treatment would add value to the decoupling indicator, as it would better reflect the real situation..