Most of its drinking water comes from the Yangtze River, Qingcaosha Reservoir, Chenhang Reservoir and upper sections of the Huangpu River. The Yangtze River Dongfengxisha Water Source Area is currently under construction.

Liu acknowledged that as the city's population grows, difficulties in maintaining water safety have increased.

"The city's increasing population has posed great challenges to the government to provide safe water for residents," Liu said. "There is a long way to go."

Environmental experts are calling for nation-level legislation to protect water sources and ensure the safety of drinking water.

Statements regarding the protection of water sources have been written into various local regulations. There are currently no specific national level laws for water source protection, experts said.

"The country's legislation on water source protection is still lagging behind. Though provinces and cities have worked out local regulations, they often fail to work when the pollution crosses boundaries," said Zheng Zheng, director of River Basin Pollution Control Research Center of Fudan University.

The problem not only exists in Shanghai, but in many other parts of the country, Zheng said.

"Pollution risks can occur in upper streams at any time, which puts pressure on the lower stream," he said. "The different responsibilities required for looking after upper streams and lower streams should be clarified through a special law."

Xia Tao, a member of the Central Committee of the Revolutionary Committee of the Chinese Kuomintang, and vice-chairman of Anhui province's Chinese People's Political Consultative Conference Committee, also called for a comprehensive management body to be placed in charge of protecting and managing drinking water sources.

The ecological protection of drinking water sources involves many aspects, such as the management of water sources, the monitoring of the whole river, a prevention system and emergency methods, he said.

While there are related laws and regulations, many are not complete and punishments are not harsh. There is also too little being done to prevent pollution, he said.