Changes in urban waste water treatment in northern European countries

• Resident population connected to wastewater collection and treatment systems reported to the "OECD/Eurostat Joint Questionnaire - Inland Waters-2012", Statistical Office of the European Union (Eurostat)

• Finland
• Iceland
• Norway
• Sweden

Methodology:
Steps for graph were set at 1970, 1980, 1990, 1995, 2000, 2005, 2010, 2012, 2014 and 2015. If data were missing for that year, the most recent year reported was used for gap filling, e.g. 2013 data used for 2014. This approach used for up to 9 years of gap filling.