The city plans to build a huge reservoir on the upper reaches of the Huangpu River to ensure clean and sufficient water supply amid growing demand, according to water authorities.

The reservoir will be almost four times of the size of the city's existing reservoir on the Yangtze River, the other major water source of the city, and could serve as a back-up reserve source in case of salt tides that endanger the water supply every winter and spring.

"Commercial water traffic poses a threat to the Huangpu water source as it's an open one, taking water directly from the river without any precipitation process before pumping the fresh water to water plants for treatment," said an official surnamed Li with Shanghai Chengtou Corporation, which manages the city's water infrastructures.

With a reservoir the fresh water will be able to undergo a self-cleaning period to cleanse some impurities, while pollutions like oil spilt by passing vessels will also cause less damage. The production cost at water plants can also be reduced with a cleaner fresh water supply.

Based on the plan, the reservoir will boast a capacity of 35 million cubic meters and it should be in the Xujing area of suburban Qingpu District. In case of an emergency shutdown of pumps for taking water from Huangpu, its reserves can ensure up to seven days of supply for water plants dependent on the Huangpu source. It is unknown when the construction can begin or complete.

The city's total water consumption this year is expected to rise three percent from last year, when the summer peak season saw the daily demand approaching its top supply capacity. The city gets about 70 percent of its water from Huangpu, with the rest coming from Yangtze, where the water is cleaner because of the much larger water flow.