Photo taken on May 19, 2015 shows one part of the South-to-North Water Diversion Middle Route Project in Xingyang City, central China's Henan Province.[Photo: Xinhua]

About 6 billion cubic meters of water has been transferred to central and northern China as of Friday via the south-to-north water diversion project, benefiting 42 million people, officials said Friday.

According to the project's construction commission office in Beijing, tap water quality in northern municipalities of Beijing and Tianjin, Hebei Province and the central province of Henan has been improving since late 2014 when water diversion began.

Eighteen large and medium-sized cities have benefited from the project. Over 70 percent of tap water supplied to downtown Beijing is "southern water," covering more than 11 million residents.

So far, more than 200 million cubic meters of "southern water" have been stored in four reservoirs in the capital.

Every year, the middle route of China's south-to-north water diversion project carries water through canals and pipes from the Danjiangkou reservoir in central China's Hubei Province to the provinces of Henan and Hebei, as well as Beijing and Tianjin.

The water transfer project was conceived by Chairman Mao Zedong in 1952. The State Council approved the ambitious project in December 2002 after nearly half a century of debate.