Reeling from three drinking water pollution incidents in the span of a month, environment officials said on Wednesday they are placing water quality at the top of their list of national environmental challenges this year.

"The outlook on water quality nationally is not optimistic, with 9 percent of the monitoring sections among the 10 major watersheds rated lower than Grade V, the worst level," Vice-Minister of Environmental Protection Li Ganjie said at a Wednesday news conference.

Experts have said the government must take tougher measures to protect sources of drinking water and expedite the construction of backup sources.