Frustration is mounting for many of the 300,000 West Virginia residents who have gone without clean tap water since a chemical spill on Thursday. Business owners with empty dining rooms and quiet aisles of merchandise around West Virginia's capital city were left to wonder how much of an economic hit they will take from the spill.

Most visitors have cleared out of Charleston while locals are either staying home or driving out of the area to find somewhere they can get a hot meal or a shower. Orders not to use tap water for much other than flushing toilets mean that the spill is an emergency not just for the environment but also for local businesses.

The emergency began on Thursday, following complaints to West Virginia American Water about a licorice-type odour in the tap water. The source: the chemical 4-methylcyclohexane methanol, which had leaked out of a 40,000-gallon (151,400-litre) tank at a Freedom Industries facility along the Elk River.

State officials said on Saturday they believe about 7,500 gallons leaked. Some of the chemical was contained before flowing into the river; it is not clear exactly how much entered the water supply.

All told, 32 people have sought treatment at hospitals for symptoms such as nausea. Of those, four were admitted to the Charleston Area medical centre but their conditions were not immediately available.

A water company executive said that it could take days before clean tap water is flowing again for about 300,000 people about 15% of the state's population in nine counties. First, water sample test results must consistently show that the chemical's presence in the public water system is at or below 1 part per million, the level recommended by federal agencies, the West Virginia American Water president, Jeff McIntyre, said on Saturday at a news conference.

The uncertainty means it is impossible to estimate the economic impact of the spill yet, particularly on restaurants and hotels, said Matt Ballard, president of the Charleston Area Alliance, the state's largest regional chamber of commerce.

"I don't know that it can be quantified at this point because we don't know how long it will last," Ballard said. "I'm hoping a solution by early next week so business can get back to normal."

Virtually every restaurant was closed Saturday, unable to use water to prepare food, wash dishes or clean employees' hands. Meanwhile, hotels had emptied and foot traffic was down at many retail stores.

"I haven't been able to cook anything at home and was hoping they were open," Bill Rogers, 52, said outside a closed Tudor's Biscuit World in Marmet, just east of Charleston. "It seems like every place is closed. It's frustrating. Really frustrating."

In downtown Charleston, the Capitol Street row of restaurants and bars were locked up. Amid them, The Consignment Company was open, but business was miserable. The second-hand shop's owner said she relies on customers who come downtown to eat and drink.

At Charleston's Yeager airport, a combined seven inbound and outbound flights were cancelled. The reason for the cancellations was an agreement between the airlines and unions for flight crews and pilots that hotels meet a certain threshold of service, and the lack of water violates the agreement, said an airport spokesman, Brian Belcher. Arrangements were being made to house flight personnel in hotels about 40 miles away.

Federal authorities, including the US Chemical Safety Board, opened an investigation into Thursday's spill. According to Department of Environmental Protection officials, Freedom Industries is exempt from DEP inspections and permitting since it stores chemicals, and does not produce them.

Governor Earl Ray Tomblin said he will work with his environmental agency chief on tightening regulation of chemical storage facilities in the current legislative session. State officials were working over the weekend on alternative sources of water that may allow restaurants to reopen. Several businesses that had arranged other sources of water were inspected on Saturday.

"We will work around the clock, 24/7, and try to open … as many businesses as possible in the next couple of days," said Dr Rahul Gupta, health officer for the Kanawha-Charleston and Putnam County boards of health.

By Saturday morning, the Federal Emergency Management Agency said it had delivered about 50 truckloads of water, or a million litres, to West Virginia for distribution at sites including fire departments.

Chris Laws found bottled water on Saturday for his two elderly nextdoor neighbours "They can't get out," said Laws, 42, of Marmet, a coalminer. "I'm keeping an eye on them. You got to watch out for your neighbours. They're the ones who are going to watch out for you."

He said he was angry at the company at the center of the leak, Freedom Industries. "A lot of people are facing bad situations because of this," he said. "They're struggling. What I don't understand is how did this happen?"