Arsenic and Old Laws
A Scientific and Public Health Analysis of Arsenic Occurrence in Drinking Water, Its Health Effects, and EPA's Outdated Arsenic Tap Water Standard
Top of Report
List of Public Water Systems in Which Arsenic Was Found in the 25 States Reporting Data
Important note regarding arsenic levels in individual water systems listed in this report
How to download the chart(s)
How to read the chart(s)
Important note regarding arsenic levels in individual water systems listed in this reportThe information on arsenic levels in public water systems included in the NRDC report Arsenic and Old Laws is derived from the U.S. Environmental Protection Agency's (EPA) 25-state arsenic database, which includes samples taken from 1980 to 1998. NRDC has not independently verified these data, which EPA collected from state drinking water program officials, and compiled into the 25-state arsenic database. Additional sampling may have been completed for some water systems after the EPA database was compiled. To verify information on all sampling completed to date for a public water system, contact your state drinking water program (call EPA's drinking water Hotline at 800 426-4791 for state contacts) or your water system.
Corrections: Because of an error in data reporting by the state of California, in the print version of this report and the earlier online version, Alameda County Water District, City of Antioch Water Department, and City of Santa Clara Water and Sewer Utilities were incorrectly included in charts identifying water systems with high average arsenic levels.
NRDC has been informed that the monitoring results reported to the state of California by the City of Milpitas, which the state then reported to US EPA (and ultimately were reported by NRDC based on EPA's database), were for emergency wells not currently in use. This information was not indicated in EPA's database. The City of Milpitas has provided information indicating that the water used by the City of Milpitas has been consistently below 2 parts per billion (ppb).
How to download the chart(s)
Appendix A is posted in downloadable spreadsheet form. We've provided the information as one master chart, and then broken it up into 25 individual state charts.
These charts have been saved as "comma delimited files," a format that can be read by most spreadsheet programs and requires the least possible download time. To download, click on any file. A new browser window will open and display a document with many rows of text and numbers, separated by commas. Under your browser's File menu, select Save As and save the file, retaining the .csv extension. Open the file in your spreadsheet program.
How to read the chart(s)
Because of the limitations of this file type, you may need to widen the columns in order to read the chart easily. To do this: When you open the chart some of the column headings will be obscured by text displayed at the top. Click into box A4 to clear the display. Then, with your mouse in the row of gray column labels at the top of the chart (A, B, C, etc.) rest it on the line between any two columns until the cursor becomes a black cross. Double click to expand the column. (Don't expand column A -- lengthy text in the first two rows will make the column too wide.)
Those column headings that may not be self-explanatory are explained below:
The following information was provided by the EPA and describes its 25-state arsenic database and conventions applied to the database:
D. "Population Served" is the average number of people who drank water from the water system during the time the sampling was done.
E. "Low Est. of Average Arsenic Level (ppb)" is a very conservative (that is, low) estimate of the average arsenic concentration, stated in parts per billion (ppb), in the system's water over the period for which data were collected by the system. EPA collected data for 1980-1998, though data were not available from all systems for this full period. The low estimate assumes that when arsenic was not reported as detected, there was absolutely no arsenic in the water at that time, even if the limit of detection was high (for example, 10 ppb), and even if other tests showed that arsenic was present in the water at levels somewhat below the previous reporting limit.
F. "Best Estimate of Average Arsenic Level (ppb) is what we believe is the most reasonable estimate of the average arsenic level in the system's tap water, based on the data available in the EPA database. In calculating the best estimate, we assume that if at least some arsenic was detected in a water system at some time, then whenever arsenic was not reported as detected, it was present at a level of one half of the reporting limit.
G. "# Samples in Which Arsenic Was Detected" lists the number of tests for arsenic in the system's water that found arsenic, according to the data in EPA's database.
H. "# of Samples in Which Arsenic Was Not Detected" lists the number of tests for arsenic in the system's water that did not find arsenic, according to the data in EPA's database.
I. "Qualifier for Minimum Level" includes two possible qualifiers for the minimum level in the next column: it can include a less than symbol ("<"), in which case the qualifier means that arsenic was not detected, with the stated detection limit. Thus, a "<" symbol in the qualifier column, followed by a 5 in the "Minimum Level Found" column, means that the minimum level of arsenic reported for the system was "less than 5 ppb."
J. "Min. Level Found" means the lowest level of arsenic reported for the system in the EPA database. If the lowest level found was a nondetect, it will be listed as <[the reporting limit]," as noted in the previous definition.
K. "Max. Level Found" means the highest level of arsenic reported for the system in the EPA database.
L. "Date Max. Level Found" means the date that the highest level of arsenic was found in the EPA database.
M. "Most Recent Sample in EPA Database (ppb)" means the level of arsenic found, in parts per billion, in the most recent arsenic test reported for that system in EPA's database.
N. "Date of Most Recent Sample in EPA Database" means the date that the most recent sample reported in the EPA database was taken.
Arsenic occurrence and exposure database description (10/19/99)
This database contains arsenic compliance monitoring data from ground and surface water community water systems in 25 States (monitoring conducted to comply with the current 50 ppb arsenic standard). Some States also provided data from non-transient, non-community water systems (NTNCWS). EPA's Office of Ground Water and Drinking Water has received this data from various sources, including States, associations, and other EPA offices. EPA has compiled the data into a single uniform format to support development of national occurrence and exposure distributions of arsenic in public ground water and surface water supplies. Below is the list of the general data conventions that were applied to the data to condition them for EPA's initial analysis. EPA will be applying additional data conventions and further manipulating the data in order to develop the national occurrence and exposure estimates, to support the arsenic in drinking water regulation proposal (January 1, 2000). In addition, these data conventions may change as EPA analyzes the data further.
Data conventions applied to the state data
1. Deleted all observations with dates before 1980, and one observation dated 2010.
2. Deleted observations with no public water supply identifier (PWSID).
3. Deleted observations from purchased water systems or inactive water systems.
4. Arsenic values reported as "zero" or non-detect ("ND") were considered to represent an analytical result below the reporting limit. If the state did not disclose the reporting limits for the samples, reporting limits were assigned based on where the majority of the lowest measured results clustered. This change was made in only two States, Alabama and Oregon.
5. Deleted samples that were non-detects with reporting limits greater than 10 ppb (e.g., <20 ppb, <50 ppb).
6. Matched PWSIDs to EPA's Safe Drinking Water Information System (SDWIS) for population served, system type, source type, system name, etc. If State had provided this information and there was a discrepancy with SDWIS, used SDWIS information for consistency.
7. Missouri reported only "detect" results to EPA. EPA's contractor contacted the Missouri Department of Health, which provided PWSIDs for all systems that monitored but had no arsenic detects for the same time period of arsenic data submitted (1/12/95-9/3/97). For each of these systems, EPA added a "non-detect" observation at the reporting limit of 1 ppb. These data were combined with the MO positive results.
For additional information on the data and how it was collected and compiled, the health risks related to arsenic in drinking water, how NRDC analyzed the data and calculated our estimates, and our conclusions and recommendations, refer to the text of this report.
Download chart(s)Appendix A master file
Comma delimited file (751K)
Zipped Excel 5.0/95 Workbook file (543K)
Individual charts for the 25 states that reported data
Get Updates and Alerts
Water on Switchboard
NRDC experts write about water efficiency, green infrastructure and climate on the NRDC blog.
Recent Water Posts
- What the Numbers Reveal About California's Water Priorities
- posted by Kate Poole, 5/18/15
- What a load of...drought relief?
- posted by Ben Chou, 5/12/15
- Reports Document Potential to Reduce Energy Costs in Affordable Housing by Billions, and How to Capture that Potential
- posted by Ariana Gonzalez, 5/12/15
NRDC Gets Top Ratings from the Charity Watchdogs
- Charity Navigator awards NRDC its 4-star top rating.
- Worth magazine named NRDC one of America's 100 best charities.
- NRDC meets the highest standards of the Wise Giving Alliance of the Better Business Bureau.