New Orleans residents from Carrollton to Village de l'Est once again found themselves clutching bottled water, taking great care as they brushed their teeth and questioning the competency of the Sewerage & Water Board as a boil-water advisory went out Wednesday morning across the entire east bank.

Prompted by another turbine failure at the S&WB’s Carrollton power plant that caused water pressure to drop throughout the system, the boil-water advisory was expected to remain in effect until Thursday afternoon.

The latest trouble followed weeks of other headline-making problems at the troubled public utility, which came under intense scrutiny in the wake of an Aug. 5 flood and revelations that top officials did not give the public accurate information about the status of the drainage system at that time.

The cause of the latest turbine problem was unknown. Only one of the five turbines at the plant was operating most of Wednesday, but the city reported about 7 p.m. that the malfunctioning turbine, No. 6, was back online, running on diesel fuel.

Until then, Paul Rainwater, a member of the interim management team at the utility, said the water and sewerage systems were using backup power from Entergy and that backup generators brought in after the flood could be used in case of heavy rains.

The turbine went offline at 7:25 a.m., and it took 20 minutes to switch to the backup power provided by Entergy while complying with internal procedures, Rainwater said. Two steam pumps intended to keep pressure in the system also did not function during the outage, he said.

That 20-minute gap was enough time for pressure in the system to drop below 15 pounds per square inch, the threshold that requires issuance of a boil-water advisory because it can allow contaminants to leach into the water in the city’s pipes.

The S&WB did not send out a notice about the pressure problems until about a half-hour after the outage, and the initial message in fact said there was no boil-water advisory in place “at this time.” A second message an hour after the pressure dropped announced the advisory.

Water samples were sent to the state for testing, a process that requires 24 hours of incubation and is not expected to be completed before Thursday afternoon.

Until the order is lifted, residents were advised not to drink tap water, brush their teeth or make ice with it, or allow it to get into open cuts or wounds. Those whose immune systems are compromised should not wash their hands, shower or bathe in tap water, the city said.

Babies and young children can be bathed if precautions are taken to ensure they don’t swallow the water, according to the city.

Water that has been brought to a rolling boil for one full minute is safe to consume.

Turbine 6 is the newest of the five operated by the S&WB. It was brought online in the past few years and typically is used to power the water and sewer systems. The S&WB decided to produce its own power because of frequent outages in the power from Entergy.

Interruptions in Entergy power were blamed for other boil-water advisories in recent years, with both utilities pointing fingers at each other for the problems.

What went wrong with the turbine Wednesday is still being investigated, city spokeswoman Erin Burns said.

Work continues on a project aimed at ending the boil-water advisories that have become increasingly common since Hurricane Katrina. Two water towers being built at the S&WB plant are designed to automatically add water to the pipes to keep the pressure up during a power outage, but those won't be completed until late 2018, Rainwater said.

In addition to the problems the boil-water advisories create for residents, they can tarnish the image the city is trying to put out to bolster tourism.

“It’s not a good look when we have to tell our guests they can’t shower, bathe, brush their teeth or drink the water. Likewise for residents,” said Kristian Sonnier, spokesman for the New Orleans Convention and Visitors Bureau. “I think it shakes our visitors' confidence in our claim that New Orleans is a world-class city.”

Follow Jeff Adelson on Twitter, @jadelson.​