BEIJING — More than 80 percent of the water from underground wells used by farms, factories and households across the heavily populated plains of China is unfit for drinking or bathing because of contamination from industry and farming, according to new statistics that were reported by Chinese media on Monday, raising new alarm about pollution in the world’s most populous country.

After years of focus on China’s hazy skies as a measure of environmental blight, the new data from 2,103 underground wells struck a nerve among Chinese citizens who have become increasingly sensitive about health threats from pollution. Most Chinese cities draw on deep reservoirs that were not part of this study, but many villages and small towns in the countryside depend on the shallower wells of the kind that were tested for the report.

“From my point of view, this shows how water is the biggest environmental issue in China,” said Dabo Guan, a professor at the University of East Anglia in Britain who has been studying water pollution and scarcity in China.