By building water filtration plants that rendered polluted river water safe to drink, if not always palatable, Philadelphia put off the need to remove pollutants entering the rivers from household and industrial sewage. Enhancements to the water treatment process were added to the filtration plants in the 1950s. A comprehensive plan for collection and treatment of the city's sewage, developed in 1914, was also fully realized in the 1950s. While the city's first sewage treatment plants removed about half of the pollutants in the waste stream, upgrades made in the 1970s and 1980s remove up to 95% of the pollutants, producing effluents that are as clean as, or cleaner than, the river water itself.