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, and for discharges to sensitive areas such as freshwater and estuaries from agglomerations of between 2000 and 10 000 inhabitants by 2005.
ELi õigusaktides on sätestatud, et 2005. aastaks tuli bioloogiliselt puhastada 10 000–15 000 linnastute kogu reovesi ja 2 000–10 000 inimekvivalendiga linnastutest tundlikele aladele (nt magevesi ja suudmealad) juhitav reovesi.