Construction work started on a water extension project on Thursday in Linqing, Shandong province, reflecting central government efforts to deal with the excessive exploitation of underground water in North China.

The water replenishment project - part of the eastern route of the South-to-North Water Diversion Project - is expected to take 21 months to complete.

It will be able to transfer 490 million cubic meters of water to the Beijing-Tianjin-Hebei region, according to the Ministry of Water Resources.

Economic and social development in North China, as well as a growing population, have brought an increasing demand for water, Jiang Xuguang, vice-minister of the Ministry of Water Resources, said at an event marking the start of the extension project.

He said water transferred by the project will replenish underground resources used by the agricultural sector, greatly easing the excessive exploitation.

Research by the Chinese Academy of Sciences published last April shows that from 2002 to 2014, about 6 billion to 8 billion metric tons of groundwater was lost annually in North China, a trend it expected to continue. Agricultural use was the main reason for the excessive exploitation.

Water transferred by the project will also replenish resources in wetland areas to improve the environment along the routes, Jiang said.

Consisting of eastern and western lines, the extension project stretches a combined 695 kilometers and is set to cost 477 million yuan ($68.1 million), said Gao Bihua, deputy general manager of China Eastern Route of Corporation of South-to-North Water Diversion.

This year marks the sixth year of the first phase of the South-to-North Water Diversion Project eastern route, which was put into operation in November 2013.

Having transferred almost 4 billion cubic meters of water to Shandong in the past six years, the eastern route has played a significant role in supplying water as well as the ecology in the province, and it has directly benefited more than 30 million people, said Yu Guoan, vice-governor of the province.