The Ministry of Environmental Protection has ordered local governments to enhance management of drinking water quality during flooding periods after a southwestern city had its main water source contaminated by waste chemicals through heavy rains, a statement said Monday.

With the arrival of this year's flood season, floods and rainfall have eroded soil and possibly washed waste from river banks into the water, thus "seriously threatening drinking-water sources," the statement said.

The ministry asks local governments to strengthen the monitoring of water quality, especially in areas susceptible to pollution, and also to provide greater supervision of factories, such as pharmaceutical, chemical, papermaking, smelting and other heavy industries.

Key pollution sources, tailings and urban sewage treatment plants are also under strict supervision, it said, adding that measures should be taken immediately if water quality is found substandard.

The warning system should also be improved so that environmental pollution incidents would be reported promptly to reduce damage, the statement said, adding that acts of covering up pollution accidents must be strongly prohibited.

Waste chemicals from the Xichuan Minjiang Electrolytic Manganese Plant in the city of Mianyang of southwestern Sichuan Province were washed into the Fujiang River, the city's main source of water, by heavy rains last month.

Mianyang residents resorted to buying bottled water after local authorities reported the contamination. The water quality alert was lifted last Friday.