(Bloomberg) -- A Shanghai official offered more assurances about water supplies for the financial hub after worries about contamination from the sea caused a brief panic, comments that come as the city builds more wells.

Ruan Renliang, deputy head of the water department, said in an interview with Bloomberg News that the sea often flows into the Yangtze River in the winter and spring because dry weather lowers levels in the major source of water for the city of 25 million people.

“The saltwater intrusion is a natural phenomenon,” Ruan said on Wednesday on the sidelines of a media event. “This year, because the upper reaches of the Yangtze River are relatively dry, there is less water coming here, which led to the earlier-than-usual arrival of salt tides.”

Shanghai residents became worried about drinking water supplies around Oct. 11 -- clearing store shelves of cheaper bottled brands -- following a report that authorities temporarily cut delivery from two reservoirs because they’d been tainted. That concern may have been amplified by memories of a virus lockdown this year when homes had trouble getting deliveries of food, bottled water and medicine.

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Salt water had flowed into the Yangtze River, Ruan said, but reservoirs were unaffected because officials closed gates in channels linking them to the longest river in Asia. He said that sea water poses a threat to Shanghai’s supplies from the Yangtze only when the flows persists for a long period, but any disruption would be eased by a reservoir linked to another river.

The city depends on four reservoirs, including the Qingcaosha, which provides the bulk of its tap water. State media has said the Qingcaosha is designed to hold 68 days’ worth of water. It was unclear how much it now has. 

The Qingcaosha and two others sit just a few meters above the East China Sea at the mouth of the Yangtze, whose levels have been lowered by a drought over the summer that domestic reports said was the river basin’s worst since 1961. The Shanghai Water Authority immediately assured the public that supplies for domestic and industrial uses were “stable,” and it had no plans to sever them.

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Still, Shanghai has announced measures to bolster water capacity since the episode. The city launched an “emergency project” to dredge the Qingcaosha reservoir, according to a document on the website of the water authority dated Oct. 12.

Officials also plan to dig a new batch of wells around the megacity’s water plants, pump stations and large residential communities to boost emergency capacity, according to the documents, and plans were also being made to upgrade some existing wells.

“This is aimed at further ensuring emergency water supply in the event of saltwater intrusion,” according to one document. 

The drought that hit the upper reaches of the Yangtze has lingered since the summer. In August, it depleted upstream reservoirs and led to a power crisis because hydroelectric dams had less water flowing through them. Key reservoirs in the region were left with about 1.2 billion cubic meters of water by late August, 4 billion less than at the same time in 2021.

Dry spells on major rivers in other countries in recent years have led to serious problems. Low water levels in in the Mekong Delta in 2016 devastated food supplies in southern Vietnam, and threatened to reduce global exports of rice, seafood and coffee.

--With assistance from Martin Ritchie.

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