Shanghai water authorities are appealing to residents to economize on water because a reservoir is facing a potential shortage during the current salt-tide season.

Experts said yesterday that four high salt tides at the mouth of the Yangtze River since October have put pressure on the Chenhang Reservoir in Baoshan District.

The most recent of the salt tides began affecting the reservoir late last week and was forecast to last nine days.

As an emergency solution, the Chenhang Reservoir has started to draw on 300,000 cubic meters of water per day from the reservoir owned by Baosteel Group Co.

"Now the reservoir's capacity can meet the daily consumption of the related districts," said an official surnamed Zhou.

"But there might be some water shortages if the tide lasts longer than our estimation."

The capacity of the Chenhang Reservoir is 1.76 million cubic meters. That's enough water for seven days.

Salty water pours into the Yangtze River mouth during the winter dry season every year from October to April, threatening water quality in the city's waterways and reservoirs.

When the density of chloride in the water exceeds 250 kilograms per liter, reservoirs have to close intake pumps to cut off the salt water.

Water shortages during the salt-tide season may soon be things of the past.

The city is building the new Qingcaosha Reservoir on the Changxing Island of Chongming County. The new facility is expected to provide water storage for up to 68 days.