Shaw resident Pamela Brown, 50, fills up bottles at a mobile water-supply station Friday. “Our water turns brown,” Brown said. “It’s good they put this up.” (Astrid Riecken/For The Washington Post)

It is common knowledge that oil and water do not mix. When they do, you should not drink it.

If that makes little sense, neither has anyone this week been able to make sense of the oil in the water that was flowing into about 350 homes in the Logan Circle and Shaw neighborhoods in Northwest Washington.

“I knew it was not a gas leak smell, but it was petroleum-y,” said Marilyn Holland, who lives on the 1200 block of Q Street.

After testing Friday, D.C. Water said the water was safe for drinking or showering, provided that people let it run for a bit to flush out the remnants of what­ever the heck it was.

“We don’t know the source, and we’re continuing our investigation,” said John Lisle, a spokesman for the water utility. He conceded that just how the oily stuff got into a closed water system was a mystery.

Felipe Marcos, one of the managers at Shaw's Tavern in Northwest Washington, used bottled water in his restaurant after a “do not drink” advisory was issued for the neighborhood. (Astrid Riecken/For The Washington Post)

Holland said her tenant first noticed a gasoline-like smell Tuesday night. On Wednesday, she thought that the pipes in her powder room smelled like petroleum. She called a contractor to look into it, but then was told by D.C. Water about the contamination Wednesday night. People were warned that using the water for showers or baths could cause skin and eye irritation.

Holland said she and her husband, Robert Nelson, do not drink D.C. water anyway, but their three cats seem annoyed by the switch from tap water to bottled.

“They’re ticked because they like to drink from the faucet,” Holland said.

Three D.C. public schools were closed by the water problem for a second day Friday. Students at Cleveland, Garrison and Seaton elementary schools got a head start on their holiday break.

Their schools fell within the endangered area, bordered by Florida Avenue and T Street to the north, Rhode Island Avenue and Q Street to the south, New Jersey Avenue to the east and 13th Street to the west.

Jackie Spindler, who lives in the 1200 block of Q Street, said D.C. Water’s advisories failed to answer her questions about the cause of the contamination or what hazards it posed.

“Their first notice was fine,” she said. “And since then it’s been like, what are we, chopped liver?”

She could not smell or see anything wrong with her water, and did not know how concerned to be.

“I took a shower this morning in dread, thinking, ‘Am I a heroic rebel or a sneaky scofflaw?’ ” she said, then asking, “Do I look dead?”

Signs on the doors of the 7-Eleven at Seventh Street and Rhode Island Avenue warned customers that many of the convenience store’s most popular items were unavailable.

“I’m not having any customers,” complained a manager, who said the company would not want him to give his name.

He gestured at the coffee, tea, soda and Slurpee stations, all covered with handwritten “Out of Order” signs.

“There’s a lot of people just walking up and turning around,” he said.

Felipe Marcos, one of the managers at Shaw’s Tavern at Sixth Street and Florida Avenue, said the restaurant had been spending about $100 a day to buy bottled water for cooking since employees learned Wednesday about the problem with the tap water.

Although they were using dozens of bottles of water to cook, Marcos said many of their regular customers were not aware of that.

At lunchtime Friday, normally a busy hour, only 16 people were eating at the 86-seat restaurant.

Eric Wingerter, a resident of the 1800 block of Sixth Street, said he was drinking and brushing his teeth with bottled water, even though he could not detect anything amiss with the water flowing out of his faucet.

“It’s the brushing your teeth that’s more challenging,” he said.

But he saw a silver lining: “if there’s been an upside to it, it’s gotten me to the gym in the mornings.” There are showers there.