โรงบำบัดน้ำเสียใหญ่ที่สุดในโลกอยู่ที่กรุงวอชิงตัน

Water flows a long and winding path from the sink to the ecosystem, but not before making an all-important stop at a waste water treatment plant. It's more than just cleaning out dirt and debris we can see; it's about removing invisible contaminants that could poison nearby waters.