The tidal phenomenon, caused by drought, is at its worst in several years with the salt water levels in some local rivers 12 times higher than standard drinking requirements, the China Daily said.

"The biggest salt water tide this year has now reached the province and it will last... until January 3," the paper quoted Guangdong's Department of Water Resources vice director Huang Qingliang as saying.

Fresh water supplies in Zhuhai and Zhongshan, two coastal cities in the province close to Macau, and Panyu district in the provincial capital of Guangzhou, will be most affected, according to the paper.

It said the salt tides, which occur when sea water floods coastal areas because of serious drought, in the Pearl River Delta region has been worsening since September.

Water levels have fallen by 52.9 percent since last year because of the drought, the China Daily said, citing government statistics.

The Xijiang and Beijiang rivers, two major tributaries of the Pearl river, witnessed their lowest-ever water levels in recent days, allowing the sea water to flow in, Huang said.

Zhuhai government has advised residents to drink bottled water instead of tap water, which mainly comes from the Xijiang river, the paper said.

Local authorities have also stopped water supplies for gardening in public areas, car washing and sauna bath businesses for one week.

Huang said serious salt tides in Guangdong could last until March next year.

Guangdong has suffered from salt tides in the past, with the most recent lasting from the end of last year until May.

Although the China Daily stated a lack of rainfall was behind the drought, environmentalists have previously said the rapid rise in the use of river and underground water by local industries is also a major factor.

The Pearl River Delta region is one of China's main economic engines, with many industries located in the area.

The salt tide situation is the latest in a spate of water problems to plague China, highlighting the growing environmental concerns as the nation pursues economic growth at any cost.

China's environmental bureau said Wednesday underground water in 90 percent of Chinese cities was polluted.

"A survey showed that underground water in 90 percent of Chinese cities has been polluted by organic and inorganic pollutants, and there are signs that (pollution) is spreading," state press quoted the State Environmental Protection Administration as saying.

The pollution is generally caused by industrial waste from factories or untreated human waste discharged into rivers and then seeping into the ground.

Underground water is the source of drinking water for nearly 70 percent of China's population, the report said.

In a separate report on Wednesday, Xinhua news agency quoted E Jingping, vice minister of water resources, as saying about 300 million Chinese rural residents, or one third of the total rural population, drink unsafe water.

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