(CNN) -- The do-not-use order issued Thursday for some 300,000 residents in nine West Virginia counties is unlikely to be lifted soon, an official said Saturday.
"I would expect that we are talking days," West Virginia American Water President Jeff McIntyre told reporters. "The timeline will vary, based on geographical location, customer demand and other factors."
Officials will know that the water is safe for more than firefighting and toilet flushing -- its only sanctioned uses now -- when tests find less than 1 ppm of 4-methylcyclohexane methanol in treated water, he said.
That is the limit below which the U.S. EPA and the Centers for Disease Control and Prevention have deemed it safe. "These agencies do not anticipate any health effect below this level," he said.
Four laboratories have been set up to measure the levels in a uniform manner. "The treatment plant must consistently produce samples at or below this level before the current do-not-use order is lifted," he said.
He said there was an inadequate number of sampling results to report current levels.
Officials from various agencies met Saturday morning to reach consensus on a plan to flush the company's water system over the coming days, McIntyre said. He predicted that the do-not-use order will be lifted in zones.
Though the water woes have led scores of businesses to close, Dr. Rahul Gupta, of the Kanawha-Charleston Health Department, said that some restaurants were reopening after devising alternative plans.
The medical impact was hard to assess. "We've had a lot of worried-well calls," he said, citing complaints of irritation of the skin, throat, chest and stomach that some residents have linked to possible exposure to the chemical, which is used to clean coal.
Water company spokeswoman Laura Jordan urged people to get medical attention "if they are feeling something ... isn't right."
Many -- perhaps too many -- did just that.
"Our emergency rooms have been very busy with individuals unnecessarily concerned and presenting no symptoms," said the Charleston Area Medical Center.
Karen Bowling, secretary of the state's Department of Health and Human Resources, said 73 people had reported to emergency departments, but that only two had been admitted to hospitals. "That's really a very small number of patients that have been impacted by this," she said.
Mike Dorsey, chief of the Department of Environmental Protection's homeland security and emergency response division, said officials estimate that 7,500 gallons -- the equivalent of about 10 hot tubs that can accommodate eight people each -- leaked through a one-inch hole in the tank's stainless steel wall.
"It's an old system," he said about the physical plant, adding that the company had planned to upgrade it.
Dorsey expressed confidence that the chemical, which smells of licorice, did not start leaking long before Thursday morning, when it was reported. "We would have gotten odor complaints earlier than that if it had been going on longer," he said.
The chemical overflowed a containment area around the tank run by Freedom Industries, then migrated over land and through the soil into the river. The leak happened about a mile upriver from the West Virginia American Water Co. plant.
After concluding late Thursday afternoon that the tap water was contaminated, a stop-use warning went out to customers in Boone, Cabell, Clay, Jackson, Kanawha, Lincoln, Logan, Putnam and Roane counties.
Since then, the offending material has been hauled from the site, officials said.
Some residents have directed their anger at the coal industry company from whose storage tank the chemical leaked.
"It's caused us more problems than you could ever imagine," said Danny Jones, the mayor of Charleston, the state's capital and most populated city. "It's a prison from which we would like to be released."
Kanawha County Commission President Kent Carper told CNN on Saturday that more than 100,000 customers were affected, bringing the number of people affected to about 300,000.
Freedom Industries also is feeling the heat.
Freedom Industries President Gary Southern tried several times Friday evening to walk away from a news conference, saying "it has been an extremely long day," only to be called back by insistent reporters -- including one who noted how long a day it has been for West Virginians without drinkable water or a full explanation as to why.
"This incident is extremely unfortunate and unanticipated," Southern said. "This has been a very, very taxing process."
Southern said two Freedom employees noticed material leaking from a storage tank into a dyke around 10:30 a.m. Thursday. They contacted authorities and began the cleanup process -- including hauling away the chemical still in the tank and vacuuming up some from the nearby ground, he said.
"We have mitigated the risk, we believe, in terms of further material leaving this facility," said the head of Freedom, which supplies products for the coal-mining industry.
The Freedom Industries president downplayed the chemical's health effects, saying it has "very, very low toxicity" and poses no danger to the public.
West Virginia American Water's McIntyre had a different take, as evidenced by the company's unprecedented stop-use warning: "We don't know that the water is not safe, but I can't say it is safe."
'I do not know how long this will last'
The federal government has gotten involved, as well, with President Barack Obama signing an emergency declaration authorizing the Federal Emergency Management Agency to coordinate disaster relief efforts.
U.S. Attorney Booth Goodwin said federal authorities are looking into what happened, telling CNN Friday that "even a negligent release of this kind could be a criminal violation."
"It's really too early to tell whether criminal charges could be brought," he said. "We're going to want to figure out just exactly what occurred and when ... But right now, obviously, what we're trying to do is get people's water back on."