Baltimore officials are advising some residents to boil water before drinking it after detecting E. coli at three addresses near Sandtown-Winchester over the weekend. Here’s what you need to know.

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What areas does this affect?

The contamination appears to be concentrated in the Sandtown-Winchester and Harlem Park neighborhoods, although Baltimore’s Department of Public Works has issued a boil-water advisory for about 1,500 homes and businesses.

The area where city officials recommend residents boil water is bounded by Riggs Avenue on the north, Carey Street on the east, West Franklin Street on the south and Pulaski Street on the west. It extends into Baltimore County, something DPW said in a release was “precautionary,” adding that recent water samples from those areas were negative for contaminants.

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What are E. coli bacteria?

E. coli refers to a large group of bacteria found in food and intestines of people and animals. According to the Centers for Disease Control and Prevention, most strains of E. coli are “harmless,” though others can cause diarrhea, urinary tract infections and other illnesses.

E. coli alone might not cause disease, said John D. Sivey, a chemistry professor at Towson University, who specializes in environmental organic chemistry and aquatic chemistry.

Rather, it’s what known as an “indicator organism” that, when detected, can signal the presence of harmful microbes that can cause disease in the water.

How was the E. coli contamination discovered?

Coliform and E. coli contaminants were discovered during routine tap water testing on Friday and confirmed through retesting on Saturday.

Contaminants were found at the Baltimore City Fire Department’s Engine 8 station, located at 1503 West Lafayette Ave.; the Baltimore Police Department station at 1034 North Mount St.; and a location at 920 North Carey St.

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How long does water need to be boiled for?

The Environmental Protection Agency advises consumers at high elevations to bring water to a boil and let it boil for three minutes, allowing it to cool before use. In case of E. coli contamination, “Boiled or bottled water should be used for drinking, making ice, brushing teeth, washing dishes, and food preparation until further notice.”

The city’s public works department has said that residents only need to boil water for one minute, given Baltimore’s relatively low elevation.

If I’m outside the affected area, should I boil water just to be safe?

The Baltimore metro area’s water system is configured in “zones,” so experts say pipes outside of one zone area shouldn’t be affected.

“I think if you’re outside of the zone, I would have no concerns drinking the tap water,” said Dr. Morgan Katz, an infectious disease expert and assistant professor of medicine for Johns Hopkins University.

What symptoms should I watch for?

Dr. Letitia Dzirasa, health commissioner at the Baltimore City Health Department, said Tuesday that infants, young children, the elderly, pregnant people and people with “severely compromised immune systems” may be more at risk of getting sick from E. coli bacteria.

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If you’ve been exposed to the contaminated water in the affected area, she said, you should monitor for certain symptoms and seek medical care if necessary.

Adults should contact a health care provider if:

They’re unable to keep liquids down for 24 hours; they’ve been vomiting or having diarrhea for more than two days; they’re vomiting blood; they’re dehydrated; they have severe stomach pain; they have a fever above 102; they notice blood in their bowel movements.

Children should be seen by a health care provider right away if they: have a fever of 102 or higher; seem tired or very irritable; are in a lot of discomfort or pain; seem dehydrated.

How did this happen?

In general, Sivey said water contamination can happen if the bacteria originated in Baltimore’s surface water reservoirs, such as Loch Raven and Prettyboy reservoirs. It’s also possible that the water leaving Baltimore’s drinking water plants were contaminated due to a structural issue such as a cracked pipe.

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“One of the main problems older cities like Baltimore have is the city has aged, and we’ve underinvested in our hundreds of miles of pipes that 2 million users rely on in the city and its surrounding counties,” Sivey said. “Oftentimes, we don’t recognize a problem until it becomes really obvious.”

Natalie Exum, assistant scientist in the Department of Environmental Health and Engineering at the Johns Hopkins Bloomberg School of Public Health, said since water in the city’s drinking water system always is highly pressurized — or, moving so quickly through the pipes that it keeps contaminants out — a contamination event could indicate a loss of pressure.

“This is an example of the system working; not of perpetual neglect, but the kind of precautionary work you do to make sure no one gets sick,” Exum said. “Given the co-located nature of the three points, it indicates there is a leak under the subsurface.”

How is the city addressing the problem?

Sivey said water treatment engineers likely are trying to “flush” the contaminated water out of the system; residents of the affected zone might notice fire hydrants opened in their neighborhoods, he said. They also might smell something in their water — likely chlorine, which water treatment engineers will use in higher quantities to ensure the harmful bacteria is killed.

How is the state responding?

The Maryland Department of Emergency Management assembled a team led by the State Emergency Operations Center Commander to “monitor events and engage other state agencies,” according to spokesperson Jorge Castillo.

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The state will also help the city fulfill its request for six certified water samplers who are trained to submit water samples to state-run labs and for two emergency manager planners. Castillo said the team is also working to help with water distribution.

Where is the city distributing water to residents?

Starting at 11 a.m. Tuesday, DPW will distribute water to residents at the following locations. Residents are encouraged to bring their own containers. Each household is limited to 3 gallons.

Are schools affected?

Baltimore County Public Schools urged 11 schools in the Southwest region to take precautions with its water, under direction of the county government. The county’s facilities management department is providing bottled water and hand sanitizer to the schools, and the school system said meals for those schools will be prepared in other facilities.

”At this time, all water samples from Baltimore County sampling sites have been free of E. Coli contamination,” the school system said in an email to the community. “BCPS will continue to follow the direction of Balt. Co public works.”

Is this related to that “Best of Baltimore” party?

Dzirasa said, at this time, “there is no evidence to suggest there is a linkage” between reports of food poisoning stemming from a recent “Best of Baltimore” party hosted by Baltimore Magazine on Aug. 18 and the current water issues in the city.

When will we know more?

In an interview on WYPR’s “Midday with Tom Hall,” DPW Director Jason Mitchell said the city will have another round of testing data Tuesday night. If the tests are negative, city and state officials will either perform additional tests or remove the boil-water advisory. If there are positive results, DPW will continue to flush fire hydrant in the affected areas and pump more chlorine into the water system to kill the harmful bacteria, and test the water three times per day.

Baltimore Banner reporters Kristen Griffith, Brenda Wintrode and Ben Conarck contributed to this article.

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