Michigan environmental regulators made crucial errors as Flint began using a new drinking water source that would become contaminated with lead, auditors said Friday, as crews in the city started to dig up old pipes connecting water mains to homes.

The report by the state auditor general found that staffers in the Department of Environmental Quality's drinking water office failed to order the city to treat its water with anti-corrosion chemicals as it switched to the Flint River in April 2014, but also said the rules they failed to heed may not be strong enough to protect the public.

Flint had been using water from the Detroit system but made the change to save money, planning eventually to join a consortium that would have its own pipeline to the lake. The corrosive river water scraped lead from aging pipes that tainted water in some homes and schools, and has been blamed for elevated lead levels in some children's bloodstreams. If consumed, lead can cause developmental delays and learning disabilities.

Crews on Friday dug up a lead service line in Flint and replaced it with a copper one at the home of an expectant couple. It marked the first residential lead pipe removal that is part of Mayor Karen Weaver's Fast Start initiative designed to replace all lead service lines in the city.

Barry Richardson II, who lives in the home with his pregnant fiancee, thanked mayor and said he no longer will "have to worry about the lead poisoning" his water.

Weaver said the work that started Friday will target lead service lines at homes in neighborhoods with the highest number of children under 6 years old, senior citizens, pregnant women, people with compromised immune systems and homes where water tests indicate high levels of lead at the tap.

More than two dozen Democrats, including House Minority Leader Nancy Pelosi, also visited Flint on Friday to hear from families affected by the water crisis. Democratic Rep. Dan Kildee of Michigan said it let lawmakers hear about Flint's problems firsthand and kept up pressure for Congress to act on a stalled bill aimed at helping the city. Kildee criticized Senate Republicans for delaying the bill and noted that lawmakers who have visited Flint in recent weeks were all Democrats.

Republican Gov. Rick Snyder, who has repeatedly apologized for the state's response, said it's taking longer than expected to locate all the lead pipes in the city but the state is working to find them.

The DEQ has acknowledged that its staffers who worked with Flint misread federal regulations designed to prevent lead and copper pollution of drinking water supplies. Three DEQ employees, including the director, have lost their jobs.

Director Keith Creagh said Friday the DEQ appreciates the auditor general's "thorough review" and "is committed to developing and implementing process and program improvements to address the findings in the report."

But the DEQ said the federal Lead and Copper Rule was ambiguous, and the auditors agreed, saying it and Michigan's Safe Water Drinking Act needed improvements. Snyder said he'd also like to set a higher water quality standard than the federal rule.

The audit said the federal rule does not require using indicators such as blood screenings to monitor for human exposure to lead. Sampling of drinking water that does take place relies mostly on samples from single-family residences, leaving out other locations such as schools and hospitals.

Additionally, many samples are taken by residents, who might use incorrect procedures, the report said.

Other DEQ shortcomings it noted included a failure to ensure that Flint drew enough water samples for testing from high-risk homes with lead pipes or fixtures. The agency said it would "put in place appropriate audit procedures that will increase the confidence and accuracy of water supply submissions."

DEQ also does not conduct surveillance visits, sanitary surveys and other monitoring within required time frames, a problem in places other than Flint, the report said. The department said 95 percent of sanitary surveys and 64 percent of surveillance visits meet required deadlines, exceeding goals set by the U.S. Environmental Protection Agency.