Urban waste water collection and treatment in Europe, 2017

Figure 1 shows the proportion of urban waste water collected and the level of treatment applied as a percentage of the population. Orange bars represent sewage collected but not treated before discharge; yellow bars represent primary treatment, such as settling; light green bars represent secondary treatment to reduce dissolved and suspended organic compounds, such as those using biological methods; dark green bars represent more stringent 'tertiary' treatment, mainly to reduce nutrients.