The town of Oak Bluffs remained under a boil water order Tuesday, as the water district waited for the mandatory 48-hour water sample testing to be completed.

Paul Provost, superintendent at the Oak Bluffs water district, said he was surprised that the Department of Environmental Protection imposed the boil water order Monday morning because while the water did contain a background coliform bacteria, the sample did not come up positive for fecal matter.

“The water is safe,” Mr. Provost said. “Just boil it, and that boiling is really a precaution. The state wants to protect all the Oak Bluffs customers like they do every other town. This is why we sampled, because if we do have a problem in the well, you want to know and you want to deal with it.”

Testing began at 8 p.m. Monday night, and results are recorded after 48 hours. The boil order may be lifted Wednesday night after 8 p.m. “Hopefully Wednesday night this goes away,” Mr. Provost said. At that point, if the water is deemed safe, the water district will most likely issue another reverse 911 notification Wednesday night or Thursday morning, pending DEP instructions.

The boil water order was issued Monday after a raw water sample from the town water supply tested positive for enterococci, according to the state Department of Environmental Protection website. Enterococci are bacteria often found in human digestive tracts, and could indicate the presence of human or animal wastes in the water. The bacteria do not pose a threat to healthy people, but can cause infections in the elderly and those who are already ill.

The announcement prompted a run on nearby grocery stores, where residents and visitors rushed to stock up on bottled water. At the Oak Bluffs library, cars queued around the block as officials handed out free gallons of bottled water. The town said it would dole out emergency water supplies between 5 and 8 p.m. Monday; and between 7 a.m. to 6 p.m. on Tuesday and Wednesday. People are asked to approach the library from Vineyard avenue to keep traffic moving during pickup times.

Joyce Kilmer-Garde, office administrator at the water district, fielded approximately 100 calls Monday from concerned residents.

There are five water sources for the town of Oak Bluffs, which are tested monthly. In the off-season the water is sampled at 17 locations, but in summer when the population swells, the water is tested at 35 sites. As a result, samples collected in the summer months are more likely to yield high bacterial counts. The Lagoon Pond well is the well in question, which testing confirmed contain coliform, a fecal indicator.

Oak Bluffs is one of few towns in the state that does not chlorinate the water. Mr. Provost said the disinfection process in Oak Bluffs is minimal. Water treatment involves “adjusting the PH and doing some phosphate control,” he said. However, each well is set up to receive chlorine should the reading on Wednesday come up positive for fecal matter.

Mr. Provost emphasized that testing is not performed on private wells, so the boil water order is not directed at those who are outside the town water system.

Ms. Kilmer-Garde urged residents to sign up for the Code Red emergency notification system online at the town’s website.

Town administrator Robert Whritenour said Monday that the state issued order as a precautionary measure. Water should be boiled for one minute before being consumed. Any ice made with the tap water should be discarded, Mr. Whritenour said, and people should not brush their teeth with tap water. Showers are okay.

A meeting was held early Monday afternoon with emergency personnel to put procedures in place.

Peter Martell, head of emergency management, said the town ordered roughly 16,500 gallons of emergency water supplies, divided into 5,026 cases.

The ban affects all buildings located in the town, including the Martha’s Vineyard Hospital and a number of restaurants and hotels.

Tim Walsh, chief executive officer of Martha’s Vineyard Hospital, said the hospital had switched over to bottled water and emptied ice machines by early Monday afternoon and had briefed staff on proper precautions. The hospital procured 250 bags of ice from an Edgartown source, a press release sent Monday afternoon said.

The hospital keeps a minimum of five days’ worth of drinking water for patients and staff on hand at all times, according to the release. Vineyard Bottled Waters also holds a reserve for the hospital, and the town had offered to assist the hospital with their bottled water supply.

Mr. Walsh said the hospital is paying close attention to the dialysis machines. The last time the town went into a boil order, dialysis patients were sent off-Island for treatment. Since then, the hospital worked with the state Department of Public Health to develop a policy that helps patients stay on-Island as long as possible.

“We do our own testing of the water on the machines; we strip them down and sterilize them and get them all set up with hourly testing,” he said. Should the tests indicate the need to send patients off-Island, the hospital would do so, he said, “but more likely than not we won’t have to.”

The dentists in the hospital will not be affected, Mr. Walsh said, because they use distilled water in their offices. The food service department had also organized to safely prepare patient meals.

Mr. Whritenour said the boil water order will be in place until at least Wednesday evening; additional testing results will indicate whether the order can be lifted at that time.

“We hope that those results will come back negative and that will allow us to lift the order,” he said.

The town used a code red reverse 911 message to alert residents, and was “invoking text messaging capabilities,” Mr. Whritenour said. Fliers were also being distributed to hotels, restaurants and institutions, and the town was working with the council on aging Monday afternoon to notify elderly residents or those who are shut in.

“We are using all of our resources to try to spread the public information as fast as we can,” he said.

The last time a boil water order was issued was late September 2009, in response to detection of coliform bacteria during routine testing. In that case, the town board of health received word from the Department of Environmental Protection via fax on a Friday evening, and therefore could not react until Monday. This time, a water commissioner came into the office in person Monday morning to notify the town.