ARSENIC IN ONSITE WATER SUPPLY SYSTEMS
Arsenic naturally occurs in earth materials such as bedrock, sand, and gravel. From these earth
materials, arsenic can be dissolved into our drinking water. Drinking water in some areas of
Kalamazoo County has levels of naturally occurring arsenic that are above the recommended health
level. Arsenic has no smell or taste in water. You cannot sense if arsenic is present without
laboratory testing. Environmental Health has bottles available for you to collect an arsenic
sample and send it to the Michigan Department of Environmental Quality (MDEQ) Laboratory for
Since arsenic is a natural part of our environment, most people are exposed to some amount of arsenic. The largest source of arsenic exposure comes from the food we eat. Some fish and seafood contain high amounts of organic arsenic. This type of arsenic is much less harmful than inorganic arsenic found in the groundwater. Fortunately, arsenic at levels found in well water is not readily absorbed by the skin; so contact with water (showering, laundering, etc.) is not a significant risk. Arsenic from a water supply does not readily disperse into the air, so inhalation during a shower or while washing dishes is not significant. Only water used for drinking and cooking is a health concern. Other exposures to arsenic include inhalation of smoke and dust from industrial processes and a small amount from tobacco smoke.
Interpretation of Water Sample Results
On October 31, 2001, the United States Environmental Protection Agency (EPA) set a maximum contaminant level (MCL) of 0.010 mg/L or 0.010 parts per million (ppm) for arsenic in drinking water. The new MCL replaces the previous MCL of 0.050 mg/L. Expressed in different units of measure, the recommended health advisory of 0.010 mg/L is the same as 0.01 parts per million (ppm), or 10 micrograms/liter (mg/L), or 10 parts per billion (ppb). The MCL serves as an advisory or recommendation for a safe drinking water level in private single-family residential water wells. Public drinking water supplies were required by law to meet the new standard by January 23, 2006.
Reducing Arsenic Exposure
If the arsenic level in your well water exceeds 0.010 mg/L, you may choose to stop using your well water for drinking and cooking, and bottled water can serve as an alternative for these purposes. Since the MCL for arsenic is a long-term exposure standard protective against cancer, and is based on consuming two liters of water per day for a 70-year period, unintentional consumption of water containing arsenic between 0.010 mg/L and 0.050 mg/L is not a significant exposure.
Connection to a community water supply system may be the most cost-effective solution. If connection to a community water system is not possible, water well replacement may be an option; however, this may not always result in arsenic reduction. Water treatment using reverse osmosis, distillation, and activated alumina water treatment devices may be the most effective and practical arsenic treatment methods for residential water supplies. Water softeners and activated carbon filters do not reduce arsenic levels effectively.
All treatment devices need regular maintenance. Failing to properly maintain a water treatment system (change filters, regeneration, etc.) may result in exposure to higher concentrations of arsenic than that coming from the well. Private water supply treatment is neither regulated nor considered a preferred permanent solution to water quality problems. Before installing a water treatment system, you should carefully research the treatment method's effectiveness for contaminant reduction and the system's operational and maintenance requirements. Treatment devices should be certified by NSF International.
US EPA Arsenic Information
USGS Arsenic Information