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Important Facts for Community Water Systems: Arsenic Concentration


Arsenic concentrations (micrograms of arsenic per liter of water or mcg/L) in community drinking water systems (CWS) are used in conjunction with information about each CWS (such as service population) to generate the following measures shown in this report: 1) statewide arsenic concentration distribution in CWSs by mean and maximum over time, 2) annual distribution of mean and maximum arsenic concentration for persons served by CWS and 3) annual distribution of mean and maximum arsenic concentration by CWS. EPHT data queries -- -- provide detailed results by year for 1) mean arsenic concentration by CWS for a select year, 2) maximum arsenic concentration by CWS for a select year, 3) mean arsenic concentration and the number of CWS by year, 4) maximum arsenic concentration and the number of CWS by year, 5) mean arsenic concentration and the number of persons served by year or 6) maximum arsenic concentration and the number of persons served by year. Additionally, users may query the number of persons served and the number of CWS in the state for a select year. A CWS is a public water system (PWS) that serves year-round residents of a community, subdivision, or mobile home park that has at least 15 service connections or an average of at least 25 residents. These CWSs are a subset of all New Mexico PWSs. To measure arsenic concentration in CWS, drinking water samples are usually taken at entry points to the distribution system or representative sampling points after water treatment has occurred.


Concentration of arsenic.


Not applicable.

Data Interpretation Issues

Measures do not account for the variability in sampling, number of sampling repeats, etc. Furthermore, concentrations in drinking water cannot be directly converted to exposure because water consumption varies by climate, level of physical activity, and between people. Due to potential errors in estimating service population, the measures may overestimate or underestimate the number of potentially affected people. In addition, the older data (i.e., 1999 through 2004) may be of poor quality that could result in over- or underestimated arsenic concentration in CWS drinking water during 1999-2004.

Why Is This Important?

Arsenic is a toxic chemical element that is naturally found in the Earth's crust, in soil, rocks, and minerals. It can also be released into the environment from agriculture and industrial activities. Arsenic can enter drinking water through the ground or as run-off into surface water sources. There is a wide variation in the levels of arsenic found in community drinking water systems' (CWS) supplies across New Mexico. In 2001 (effective January 23, 2006 for surface water- and 2007 or 2008 for ground water-supplied CWS), the Environmental Protection Agency (EPA) reduced the regulatory drinking water standard or Maximum Contaminant Level (MCL) from 50 micrograms per liter (mcg/L) to 10 mcg/L on the basis of bladder and lung cancer risks. People who drink water containing arsenic in excess of EPA's standard and over many years could experience skin, cardiovascular, neurological , liver, and kidney problems; they also may have an increased risk of diabetes and of developing certain cancers (such as bladder and lung cancers). Community systems' drinking water is routinely monitored and tested for arsenic by CWS to comply with the 10 mcg/L EPA standard for arsenic. (A CWS is a system that serves at least 15 locations or 25 people year-round, including most cities and towns, apartment buildings, and mobile parks with their own water supplies.) Every year, CWS send to their customers a consumer confidence report (also called a water quality report) that lists any levels of arsenic detected. EPA also requires all CWS to give their customers public notice when their water supply violates the arsenic standard. This would include information about what is being done to correct the situation. However, people who use their private wells water for drinking are solely responsible for testing the water for arsenic (for information about laboratories certified to test drinking water and certified home treatment units visit

Other Objectives

CDC Environmental Public Health Tracking, Nationally Consistent Data and Measures (EPHT NCDM)

Health Program Information

Arsenic measures are developed from CWS water quality data stored in the New Mexico Safe Drinking Water Information System (SDWIS) database, which is managed by the New Mexico Environment Department's Drinking Water Bureau. All CWS are required to monitor for arsenic; however the frequency of monitoring varies depending on source water type and the level of arsenic observed in past samples. Routine, required monitoring is annual for surface water sources and once every three years for ground water sources of drinking water, with a quarterly monitoring if a sample exceeds 10 mcg/L. With a state-granted monitoring waiver, the sampling frequency can be reduced to once every nine years.
The information provided above is from the New Mexico Department of Health's NM-IBIS web site ( The information published on this website may be reproduced without permission. Please use the following citation: "Retrieved Wed, 22 September 2021 from New Mexico Department of Health, Indicator-Based Information System for Public Health Web site:".

Content updated: Wed, 17 Apr 2019 11:28:23 MDT