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How we analyzed lead test results


For our special report on lead in the water at California schools, EdSource compiled data on the results of tests for lead in water from more than 3,700 of the state’s over 10,000 schools from the last two years.

A new state law gives schools until July 1, 2019, to have their water tested for lead. 

The law exempts schools built or modernized since 2010 and schools already testing their water. Private schools are also exempt, but can request the free testing, which water utilities started offering in 2017.

The database includes results from more than 2,700 schools in about 300 school districts and nearly 1,000 schools in Oakland, San Diego and Los Angeles. It also includes 174 of the state’s more than 3,000 private schools.  EdSource’s database includes results from August 2016 through May 20, 2018.

The test results were compiled from four sources:

  • The California State Water Resources Control Board, which collects test results from schools tested by their local water agencies. The analysis includes data through June 1, 2018. Monthly updates of test results are available on the board’s website.
  • Los Angeles Unified School District data was provided in response to a request under the California Public Records Act. The data cover the period 2008 through May 20, 2018.
  • Oakland Unified School District makes the results of its testing available on its web site. The database includes results as of April 13, 2018.
  • San Diego Unified School District results are as of June 15, 2018 and are available on the district’s web site.

In situations where the local water agency and the district both conducted tests at a school, those results were combined for analytical purposes. In the map and database the highest test result and highest active lead level are the highest of all tests regardless of who conducted it.

The map and database data include all schools regardless of type. This includes traditional public schools, charter schools both on and off district property, private schools, district-run child care centers, and other district-owned buildings.

Los Angeles Unified’s practice has been to remove test results from its web site once a water fixture has been shut down. The web site lists only the most recent test at each active fixture. As a result there are some test results that show up on EdSource’s map and database but are not found on the district’s web site. EdSource’s data, obtained from the district, are as of May 20, 2018.