CHINA - More than half of underground water monitored in China last year was low quality, according to a government report released on Tuesday.
Findings in the Report on China's Environment Condition are based on 4,929 monitoring stations in 198 prefecture-level areas.
The report, released by the Ministry of Environmental Protection, shows that underground water quality at 1,999 stations - 40.5 per cent - was "bad", while the quality at 826 stations - 16.8 per cent - was graded "worst".
Underground water quality at other monitoring stations was excellent or good, according to the report.
Some of the major problems with the water that failed to meet quality standards include excessive levels of chemicals, such as fluoride, ammonia nitrogen and chloride.
Water quality at 793 stations was improving, while it was becoming worse at 910 stations, the report said.
Underground water quality can easily be affected by many factors, including pollution caused above ground, said Xiong Yuehui, director of the Ministry of Environmental Protection's Supervision Center for North China.
Besides sewage discharged by companies, polluted water in rivers and lakes can also taint underground water, he said.
"As long as rivers and lakes flow with pollutants, most of which are discharged by enterprises, these water will pollute underground water," Xiong said.
Rivers and lakes in China are slightly polluted in general, according to the report.
Residents in more than 400 cities have underground water as a source of drinking water, and underground water provides an estimated 20 per cent of water supply in China.
Most efforts should be focused on preventing underground water from becoming polluted, since improving the quality of polluted underground water is very difficult and can be extremely costly, experts said.
"Solutions to polluted underground water are very limited," said Sun Jichao, a senior engineer in underground water research at the Chinese Academy of Geological Sciences.
"Pollution prevention should be a priority for underground water management."
The Ministry of Environmental Protection urged local authorities in May to intensify supervision and law enforcement on enterprises that illegally discharge sewage underground, after media reports that factories in Weifang, Shandong province, had been discharging sewage underground through deep wells.
During a campaign to fight underground water pollution in February and March, the ministry punished 55 enterprises in six provinces and municipalities in North and Central China that used seepage wells or ditches to transmit or store sewage, the ministry said.