Waste water in European countries From waste water collection and treatment to discharges Maria Pau Vall 77 % of the EU population is connected to public waste water treatment plants A large part of the water abstracted for domestic, industrial or agricultural use is returned to the environment (to rivers, lakes or directly to the sea) as waste water with impaired quality. Public sewerage collects domestic effluent, together with industrial waste water and/or run-off water. Sewage treatment systems, when efficient, preserve the health of water resources, the soil and human health. in focus Towards the end of the 1990s around 80 % of European Union population was connected to public sewerage systems, and 77 % to waste water treatment plants. In Candidate countries less than 55 % of the population is connected to public sewerage systems and only 45 % to waste water treatment. In the EU over the last 15 years there has been a shift from mechanical (primary) sewage treatment towards biological (secondary) and/or advanced treatment ENVIRONMENT AND systems (tertiary) while in Candidate countries mechanical and biological treatment are ENERGY predominant.