D.C. Water and Sewer Authority General Manager David Gadis said his agency did the best it could with the technology at its disposal to alert residents to potential water contamination in July. (Michael S. Williamson/The Washington Post)

D.C. Water and Sewer Authority officials pledged Thursday to revamp their systems for communicating with the public after an internal report identified multiple shortcomings in the way it handled a potential contamination of the city’s water supply last month.

The report — which includes recommendations for improving the agency’s oversight of the water system and protocols for alerting D.C. residents of emergencies — offers the most thorough accounting to date of events that led to tens of thousands of people being warned against drinking their tap water over two days in mid-July.

It shows prolonged delays in the agency’s reaction to news that an error by a utility worker led to dangerously low pressure in pipes serving about 34,000 addresses in Northwest and Northeast Washington. More than 100,000 residents and visitors were probably affected by the problem, the report states.

It took almost six hours after the incident for utility officials to prepare an advisory warning customers to boil their water before drinking it and a map of the endangered area — too late for many who had already consumed tap water.

And the warning was delivered haphazardly. The agency posted warnings on Twitter and advised news organizations of the problem. But its website became unusable because of loading delays as customers sought information on the morning of July 13, and the automated calling system deployed by the agency worked far too slowly, leaving many without timely notification.

The notification problems caused widespread anger and alarm, as families complained that they began using their water before receiving the warning.

No one ultimately reported getting sick, although the new report states that the water collected at one hydrant on the day the alert went out tested positive for coliform bacteria. The alert was lifted July 15, after a second round of tests showed no contamination.

To remedy such problems, the report states, D.C. Water has added a second Web server to deal with high traffic on its site and is in the process of replacing its robo-call system with technology that can reach customers faster.

The agency is also discussing the possibility of issuing wireless emergency alerts — similar to warnings about suspected kidnappings and flash floods — with the D.C. Homeland Security and Emergency Management Agency (HSEMA).

The employee whose error created the water-pressure problem resigned from D.C. Water this week, agency spokesman John Lisle said.

David Gadis, the utility’s general manager, said Thursday that he stood by his assertion immediately after the episode that D.C. Water “did everything that was possible and in our power” to alert its customers.

“The tools that we had before us on that day — we utilized all those tools,” he said. “Now, were all those tools effective? No.”

D.C. Water board chairman Tommy Wells said the agency’s handling of the boil-water alert “does not meet the expectations of the board” and “put everyone on notice that the emergency communications for water safety are not adequate.”

Wells said the improvements outlined in the report will help address those concerns.

“We expect a far more robust response based on today’s capacity of technology, not yesterday’s,” he said.

Problems began about 8:30 p.m. on July 12, when the utility worker opened the wrong valve at Bryant Street Pumping Station, causing pressure to drop in water pipes serving a belt of the city from the Potomac River in Northwest to the District’s border with Prince George’s County in Northeast. The report states that the employee “has given inconsistent responses as to why he opened the valve.”

The valve stayed open for an hour. Between 8:45 and 10 p.m., D.C. Water’s emergency command center received 483 calls, only 47 of which were answered by two overwhelmed dispatchers, according to the report.

Emails obtained by The Washington Post through a public-records request show that Children’s National Hospital, the VA Medical Center and MedStar Washington Hospital Center reported to the utility low or no water pressure. MedStar began diverting its trauma patients to other hospitals.

Low pressure can also allow groundwater to seep into pipes, creating a risk of contamination. At 11:50 p.m., after a preliminary consultation with the U.S. Environmental Protection Agency — the regulatory body overseeing the utility — D.C. Water informed the EPA that it would put out a precautionary directive for residents in the affected area to boil tap water.

But it was not until 3:30 a.m. that the advisory was ready to put out.

During that hours-long stretch, according to the report, utility officials were trying to prepare a legible map of the affected area and were consulting with the EPA on the language in the boil-water warning.

About 3:50 a.m. the warning was sent to news organizations, and at 4 a.m. it was posted to D.C. Water’s website. However, as more and more customers checked the site it became overwhelmed, with load times of more than one minute. A second server was installed to improve its performance, but not until 1 p.m.

The utility’s robo-call system was activated at 6 a.m. to reach people as they were waking up. Officials scheduled 26,000 calls through the system. However, it was capable of making only about 1,200 calls per hour. Some customers said they never received a call.

The D.C. government also pitched in, with HSEMA sending a warning via a subscription alert service and D.C. Fire and Emergency Medical Services posting the advisory to the neighborhood social network Nextdoor.

The emails obtained by The Post show that utility officials were also scrambling to translate their advisory for customers who don’t speak English. A staff member for D.C. Council member Brianne K. Nadeau (D-Ward 1) asked utility officials for a translation into Amharic, the language spoken by many East African immigrants in her ward.

About an hour and a half later, D.C. Water spokesman Vince Morris forwarded the request to HSEMA, which forwarded it in turn to the mayor’s office. The warning was ultimately translated by the mayor’s Office on African Affairs, but it wasn’t ready until 1:27 p.m.

Council member Mary M. Cheh (D-Ward 3), chairman of the council’s Committee on Transportation and the Environment, said she thought the water authority’s proposed improvements — on which she was briefed at a Monday meeting with other city officials — would address concerns she expressed immediately after the incident.

“There were a number of things that we talked about that I feel pretty confident, if they’re put in place, and we’re erring on the side of caution, we should have a much, much better response,” Cheh said.

“We were lucky — very, very lucky,” said Cheh, one of many residents who drank tap water before learning about possible contamination. “Out of all the kinds of things that could have happened, this is probably the most benign, and it gave us a chance to make these improvements.”