EU law stipulates that secondary treatment had to be in place for all wastewater from agglomerations with a of between 10 000 and 15 000 inhabitants by 2005, and for discharges to freshwater and estuaries from agglomerations of between 2000 and 10 000 inhabitants.
ELi õigusaktides on sätestatud, et 2005. aastaks tuli bioloogiliselt puhastada 10 000–15 000 linnastute kogu reovesi ja 2 000–10 000 inimekvivalendiga linnastutest magevette ja suudmealadele sattuv reovesi.