Arsenic in Your Well Water

A new study from the U.S. Geological Survey and Centers for Disease Control and Prevention was released last month. The author estimates that about 2.1 million people in the U.S. may be getting their drinking water from private domestic wells considered to have high concentrations of naturally occurring arsenic, presumed to be coming primarily from rocks and minerals through which the water flows.

About 44 million people in the lower 48 states use water from domestic wells,” said Joe Ayotte, a USGS hydrologist and lead author of the study. Private wells are the dominant source of drinking water for people living in rural parts of the United States. In most of the U.S., domestic well water quality is not regulated; it is up to the well owner to understand the arsenic hazard and other water quality hazards and take steps to test their water and treat it if necessary. This study is a good reminder that prudent, routine testing of the water is an essential first step for these homeowners and their families.

Using water samples from more than 20,000 domestic wells, the researchers developed a statistical model that estimates the probability of having high arsenic in domestic wells in a specific area. The researcher used a standard of 10 micrograms of arsenic per liter -- the maximum contaminant level allowed for public water supplies and used it developed maps of the contiguous U.S. showing locations where there are likely higher levels of arsenic in groundwater, and how many people may be using it. They used that model in combination with information on the U.S. domestic well population to estimate the population in each county of the continental United States with potentially high concentrations of arsenic in domestic wells.

Much of the country is potentially impacted by arsenic and is a national public health concern. Some of the locations where the authors estimated the most people have high-levels of arsenic in private domestic well water include:

• Much of the West – Washington, Oregon, Nevada, California, Arizona, New Mexico
• Parts of the Northeast and Midwest – Maine, Massachusetts, New Hampshire, New Jersey, Maryland, Michigan, Wisconsin, Illinois Ohio, Indiana
• Some of the Atlantic southeast coastal states – Florida, Virginia, North Carolina, South Carolina

Long-term exposure to arsenic in domestic wells may cause health-related problems, including an increased risk of cancer. Recent work in the U.S. also indicates that low-level arsenic may impact fetal growth and may be related to preterm birth. Public water supplies are regulated by the U.S. EPA, but maintenance, testing and treatment of private water supplies are the sole responsibility of the homeowner. Though about 44 million people in the U.S. get their drinking water from private wells, surveys indicate many homeowners are unaware of some basic testing that should be done to help ensure safe drinking water in the home.

Like may other contaminants, high concentrations of arsenic in water do not effect taste or smell, the only way to know how much arsenic is in drinking water is to have it tested. Testing you well is the first step in ensuring the safety of your drinking water supply. After testing it may be necessary to treat the water to reduce or eliminating the health risks or concerns.

You may wish to consider water treatment methods such as reverse osmosis, ultra-filtration, distillation, or as a last choice ion exchange. Typically these methods are used to treat water at only one faucet. Though anionic exchange systems (water softeners) are whole house systems, they may not be the best choice. These systems use a physical/chemical process to exchange ions between a resin bed and water passing through. These systems can remove calcium carbonate, iron and manganese, and lower nitrate and arsenic levels. Specific contaminant removal is determined by the composition of the resin bed used. Other constituents in water can compete with arsenic for the resin sites reducing the systems effectiveness. Also, depending on your water chemistry, they may create other problems.

To understand the risk and to make progress on reducing exposure in a systematic way, we need better understanding of groundwater chemistry and estimates of the population affected by high arsenic concentrations and other contaminants. The work by the USGS and the Virginia Household Quality Program accumulates data and helps homeowners identify these risks.