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  • David Smyth

What is Arsenic? How Does It Get In My Drinking Water?

Updated: Nov 18, 2022

What is arsenic?

Arsenic is a naturally occurring metalloid found in rocks, soil, water, air, plants and animals. It occurs in both organic and inorganic forms. Inorganic arsenic is highly toxic. While not as toxic, organic arsenic is still dangerous, and is used as a pesticide and herbicide.

Due to its potency, discreetness, and availability, arsenic was frequently used as a poison. Inorganic arsenic compounds such as arsenic trioxid are odorless and tasteless. Arsenic poisoning was difficult to detect as the symptoms initially mimicked food poisoning, but a single dose could produce severe diarrhoea and vomiting, paralysis, and death. As it was a favored weapon of the ruling class, it was known as the “poison of kings” or the “king of poisons.”

Despite its well-known toxicity, arsenic was popular during the Victorian era. Doctors prescribed it as treatment for a variety of conditions, including rheumatism, worms and morning sickness. Arsenic was also used in beauty soaps to improve complexion and was even reported to increase libido. Predictably, use of these products often led to painful and even fatal results.

How does arsenic get in drinking water?

Arsenic easily dissolves in water. Most arsenic enters water supplies either from natural deposits in the earth. Certain portions of the US have a naturally high level of arsenic in the groundwater, as water passes through arsenic deposits.

Arsenic is also used in industry and agriculture, and even residential purposes. As recently as 2003, arsenic was used to treat lumber. Outdoor structures, such as decks, play equipment, and furniture made around or before this time may contain arsenic, and can leach into the groundwater supply.

In the 19th and 20th century, American farmers relied heavily on arsenic-containing pesticides. While most forms of arsenic are currently banned, residues remain in older farmland. In addition, monosodium methyl arsenate (MSMA) is still in use, especially where weeds have developed resistance to modern herbicides. Farmland contaminated with organic arsenic can leach into the groundwater supply.

Arsenic is used industrially as an alloying agent, as well as in the processing of glass, pigments, textiles, paper, metal adhesives, wood preservatives and ammunition. It is also a byproduct of copper smelting, mining and coal burning. U.S. Industries release thousands of pounds of arsenic into the environment every year.

Fish, shellfish, meat, poultry, dairy products and cereals can also be dietary sources of arsenic, although exposure from these foods is generally much lower compared to exposure through contaminated groundwater. In seafood, arsenic is mainly found in its less toxic organic form.

What are the health effects of arsenic exposure?

Inorganic arsenic is a known carcinogen. According to the World Health Organization (WHO), the immediate symptoms of acute arsenic poisoning include vomiting, abdominal pain and diarrhea. These are followed by numbness and tingling of the extremities, muscle cramping and in extreme cases, death.

Long-term exposure to high levels of inorganic arsenic (e.g. through drinking-water and food) are usually observed in the skin, and include pigmentation changes, skin lesions and hard patches on the palms and soles of the feet (hyperkeratosis). These occur after a minimum exposure of approximately five years and may be a precursor to skin cancer.

In addition to skin cancer, long-term exposure to arsenic may also cause cancers of the bladder and lungs.

Other adverse health effects that may be associated with long-term ingestion of inorganic arsenic include developmental effects, neurotoxicity, diabetes and cardiovascular disease. In China (Province of Taiwan), arsenic exposure has been linked to “blackfoot disease”, which is a severe disease of blood vessels leading to gangrene. However, this disease has not been observed in other parts of the world, and it is possible that malnutrition contributes to its development.

How do I avoid arsenic exposure?

Avoid drinking water or preparing food with water containing elevated levels of arsenic. In the US, the EPA has established a Maximum Contaminate Level (MCL) for arsenic of 10 parts per billion. Municipal water suppliers are required by law to conform to EPA standards. However, not all water suppliers conform to EPA standards. Be sure to verify your water supply is safe. If your municipal water has elevated levels of arsenic, you may have to contact your state health agency or the EPA.

Well-water owners are not required to test their water. However, it is recommended to test water annually to determine if arsenic levels are a concern.

If your water supply contains elevated levels of arsenic, avoid drinking water or using water for food preparation. Home filtration systems like the Smyth/Cid Water Filtration system utilizes AquaCera Cerametix filters, which are rated to reduce arsenic by 95%.

It is important to note that with any carbon filtration system, contaminate reduction will slowly diminish over time, which is why it is recommended to change your filter on a regular basis.

Certain foods may also be a source of arsenic. While most foods can contain arsenic at some levels, rice is one of the greatest potential sources. Rice is of particular concern because of the way rice is cultivated. Rice fields are flooded, requiring greater irrigation and greater potential arsenic contamination. In addition, rice absorbs arsenic more readily than other crops. Consumer Reports has established recommendations on which rices to avoid and how much rice should be in your diet.

Please note: articles on are intended for informational and educational purposes only. Please consult your regional public health official for information regarding the safety of your water supply. In addition, please consult a medical health professional regarding specific concerns regarding arsenic.


  1. Basic Information about Arsenic in Drinking Water, EPA:

  2. Arsenic in Drinking Water, NRDC:

  3. Arsenic, WHO:

  4. Arsenic – the “Poison of Kings” and the “Saviour of Syphilis,” Journal of Military and Veterans’ Health:

  5. Arsenic In Agriculture Enjoys Comeback In Poultry Feed, Pesticides, Huffington Post:

  6. How much arsenic is in your rice? Consumer Reports:

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