sentences:  In analogy to the blue drop certification system for drinking water, the government has launched a green drop certification for municipal wastewater treatment.As of May 2011, 7 out of 159 water supply authorities were certified with the green drop, and 32 out of 1,237 wastewater treatment plants.In 2009, when 449 wastewater treatment plants were assessed, according to official government data 7% were classified as excellently managed, 38% "performed within acceptable standards" and 55% did not perform within acceptable standards.