Chicago Public Schools has been testing lead levels at city schools over the past several months. Pictured, the National Guard hand out water testing jugs for residents at a fire station January 21, 2016 in Flint, Michigan. View Full Caption Getty Images

CHICAGO — Twelve Chicago Public Schools have found elevated levels of lead in their water since testing began district-wide last month — one in every five of schools tested so far.

And test results haven't come back yet for hundreds more schools.

The results come as the district "is taking proactive steps to ensure that our children's drinking water is safe across all schools," said spokesman Michael Passman.

The schools testing positive range from Andersonville to Morgan Park. So far, 11 schools have tested above federal limits of 15 parts per billion, or .015 milligrams of lead per liter of water. The 12th school, Reilly Elementary, is being retested following concerns the test might not have been accurate.

Ariel Cheung on the lead testing at CPS schools.

The remaining 11 schools include: Beidler Elementary; Brentano Math and Science Academy; Budlong Elementary; Harvard Elementary; Esmond Elementary; Fernwood Elementary; Lasalle II Language Academy; Josephine Locke Elementary; Peirce School Of International Studies; Perez Elementary and Tanner Elementary.

So far, 58 schools have received results of the lead testing, which has included 15,853 samples of water sources as of June 7. Of the 3,044 samples with results so far, 70 have shown actionable levels of lead, roughly 2 percent.

The tainted samples came mostly from drinking fountains, along with one kitchen sink and four other sinks, CPS said. Any schools with samples above federal standards will have water shut off until the issue is addressed.

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Half the 12 schools had just a single source of contamination, with some barely exceeding the acceptable levels of lead found in water.

Tanner Elementary was the first school to test positive. The South Side school, 7350 S. Evans Ave., also had the most sources above acceptable levels and had the highest amount of lead. The 114 parts per billion found in a water fountain is seven times the allowed limit.

Perez Elementary School in Pilsen came close to Tanner, with five samples in the annex basement testing between 24 and 108 parts per billion of lead. Beidler Elementary in East Garfield Park had five samples that tested between 24 and 111.

Three samples at Brentano had lead levels between 16 and 55 parts per billion.

Another 13 schools had some lead in their water samples, but were below the federal threshold for allowed levels. Burroughs Elementary School in Brighton Park, for example, had traces of lead in all 45 of its samples, with the highest result at 2.17 parts per billion.

Water faucets and fountains were shut off at Reilly Elementary School, 3650 W. School St., in Avondale and Peirce School of International Studies, 1423 W. Bryn Mawr Ave., in Andersonville.

Reilly sent home a letter to parents and issued automated phone calls explaining the situation on Tuesday, the same day it received the results, CPS said. District officials believe the elementary school's water might have been turned off a few days before the initial samples were taken.

That "would have a significant impact on results," CPS said.

The call told parents "we received results for Reilly that indicated levels above the EPA's action level, but we are concerned that there may be anomalies and are doing an immediate retest to better understand the situation," according to a script provided by CPS.

The school supplied bottled water for students and placed water coolers next to every fountain in the school.

Reilly Principal Ken Fitzner did not respond to requests for comment.

The city Water Department assessed the situation Wednesday, with results expected by the end of the week.

At Peirce, a parent was told elevated levels were found in one water fountain and a note would go out to families Thursday.

Students confirmed at least two water fountains were shut down at the school Wednesday. Peirce Principal Lorianne Zaimi was not immediately available for comment.

It was not immediately known what levels of lead were found in the schools.

CPS Chief Executive Officer Forrest Claypool called for district-wide testing in late May after Tanner Elementary tested positive last month as part of a pilot program. The district began by testing 324 schools built before 1986 with pre-kindergarten programs.

The government is especially concerned with children drinking lead-tainted water, as they're more susceptible to its effects. Amounts of lead that won't hurt adults can hinder mental and physical development in children, according to the Environmental Protection Agency.

While no level of lead is totally safe when found in drinking water, experts say hand-washing or other contact exposure is not harmful.

Concerns over lead poisoning stemming from the rampant lead-related issues in Flint, Michigan, pushed CPS to test 32 schools in April before expanding the program to every school in the district before the end of the school year. In Flint, nine in 10 homes tested had lead values averaging 25 parts per billion.

RELATED: High Lead Levels Found At CPS Elementary, All Schools Will Now Be Tested

Of those first Chicago schools tested, Tanner Elementary was the only one to exceed federal standards for the presence of lead in water. Six met federal standards, while 25 have no lead whatsoever in the water.

The district pledged to notify students' families, supply bottled water for children and make repairs at any school with lead found in the water. The results are also supposed to be posted online.

Last month, Ogden International School said it passed recent tests for lead poisoning at both its campuses.

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