Change in urban waste water treatment in European countries, 1990-2017

Note:
Figures show the improvement in collection and level of treatment of sewage over time. The proportion of urban waste water collected, and treatment levels applied, are shown as a percentage of the population. Initially, collecting systems for sewage need to be built (orange bars), followed by primary sewage treatment such as settling (yellow bars). Secondary treatment of the waste water to reduce dissolved and suspended organic compounds, such as those using biological methods, are shown by light green bars, while more stringent "tertiary" treatment to reduce mainly nutrients is shown by the dark green bars. Grey bars show where the type of treatment was not specified.