The Associated Press

Lead Sampling Results at WHO's recommended 10 ppb limit


Michigan's governor has proposed dropping the over-rate limit for lead in drinking water from 15 parts per billion to 10 parts per billion. An AP analysis has found if that rule were to go into place nationwide, more than 2,500 water systems serving 18 million Americans would have violated the standard from the beginning of 2013 through 2015. That's a significant increase from the 1,477 water systems found over-limit during that time period under the current rule.

About the data set

The data set, which now includes results of sampling tests through December 31, 2015, summarizes lead sampling results from the EPA's Safe Drinking Water Information System. Be aware that these results are self-reported by water systems and there are some extreme outliers in the data which may have resulted from input errors. The AP analyzed 25 years of sampling data reported by roughly 75,000 drinking water systems that are subject to the lead rule, which went into effect in 1991.

While no lead exposure is considered safe, the current federal rule calls for water systems to keep lead levels below 15 parts per billion. World Health Organization officials recommend levels below 10 parts per billion, a standard adopted by many other countries across the world, including China, Canada and the members of the European Union.

How lead sampling works: Water officials collect anywhere from 5 to over 100 samples from taps across their system. The lead sampling result is reported as the 90th percentile of those samples -- meaning that 10 percent of tap samples are above the reported level, and 90 percent are below. If this result is above the federal 15 ppb level, water officials need to inform customers about the problem and take steps to address it, such as by adding corrosion control treatment to keep lead from service lines from leeching into the water. Samples are taken at taps at residential, commercial and government sites - the number of samples required is based on how many customers the water system serves.

Our analysis reports the singular 90th percentile result of a lead sampling period, and not the individual samples collected from taps. We deleted duplicate records of samples that covered the exact same sampling period with the same results and corrected known reporting errors for about two dozen systems within the data set.

Included spreadsheets

State-by-State count: The first spreadsheet counts the number of water systems in each state that would have been over-limit in the past three years if the WHO's recommendation of a level of 10 parts per billion level had been in place. It also includes a count of how many water systems had action exceedance levels during that time period under the current federal limit of 15 ppb.

Download the state count file: here

Over-limit water systems at 10 ppb: The second spreadsheet provides data on each water system that has had a lead sampling result over 10 parts per billion from Jan. 1, 2013 to December 31, 2015. This includes the name of the water system, the dates of the most recent sampling period, the sample results at the 90 percentile benchmark, and the total number of sampling periods where a limit of 10 ppb has been exceeded since 2013 and since sampling began in late 1991. Extremely high results (above 50 ppb) should be double-checked with the agency for possible errors in reporting. It also includes a flag if the system in the past three years has had a sampling period over the current federal limit of 15 ppb.

Download the over-limit sample file: here


The EPA's SDWIS lookup tool for Lead and Copper samples is here. You can use this tool to check on all sampling results from your local water system -- enter your local system's Pwsid from the attached lead sample file into the "PWS ID" field and delete the Sample End Date, then click on "View Reports" to see all samples taken at your local system. PLEASE NOTE: The samples reported on the EPA's website are expressed in milligrams, not micrograms (parts per billion). To get the proper ppb level, multiply the EPA site's results by 1,000. If this number is over 15, it is over the action limit. (This should also then match the spreadsheet numbers, which are properly recorded in parts per billion).

This data is reported to the EPA by state enivornmental agencies. There are some issues with misplaced decimals in the sampling data, and extremely high results should be regarded with suspicion. A spot-check of some of the largest outliers in the dataset found that most had a decimal-point error. In the cases where the AP found an error and received the actual sampling results, the data has been corrected (these changes were made in the case of roughly two dozen water systems). Please call the water system involved to double check before reporting results that are many times over the federal limit.

The state and city is where the administrator of the water system is located. In nearly all cases, these are the same as where the water system is located. In some cases, a water system may serve customers in multiple states. And in the case of multi-state companies - or very small systems - the administrator may be off-site. The PWS_location field is the state where the system actually is, and should be used for counting the number of systems by state.

The Associated Press analysis on the original story published on April 9, 2016 used a data set only current through the end of September 2015. This analysis includes data through the end of the year.

Column Definitions, State Count

Column Definitions, Over-Limit Water Systems

All data collected and prepared by AP Data Journalist Meghan Hoyer.