Arsenic contamination of groundwater is a form of groundwater pollution which is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater. It is a high-profile problem due to the use of deep tube wells for water supply in the Ganges Delta, causing serious arsenic poisoning to large numbers of people. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water. The problem became a serious health concern after mass poisoning of water in Bangladesh. Arsenic contamination of ground water is found in many countries throughout the world, including the US.

The World Health Organization recommends limiting arsenic concentrations in water to 10 μg/L, although this is often an unattainable goal for many problem areas due to the difficult nature of removing arsenic from water sources.

Approximately 20 major incidents of groundwater arsenic contamination have been reported. Locations of potentially hazardous wells have been mapped in China.

Gold mining can contaminate groundwater with arsenic, because the element typically occurs in gold-containing ores. Gold processing releases arsenic from mine tailings, and contaminated groundwater may be unsafe to drink for decades. Arsenic that is naturally occurring can contaminate the soil, just as it does the groundwater. This presents a possible arsenic exposure by use of products containing tobacco, because the tobacco plant grows from the soil and can become infiltrated with the arsenic.

Arsenic contaminated water typically contains arsenous acid and arsenic acid or their derivatives. Their names as "acids" is a formality; these species are not aggressive acids but are merely the soluble forms of arsenic near neutral pH. These compounds are extracted from the underlying rocks that surround the aquifer. Arsenic acid tends to exist as the ions [HAsO₄]²⁻ and [H₂AsO₄]⁻ in neutral water, whereas arsenous acid is not ionized.

An analysis of water and food consumption in Socaire, a rural village in Chile, found that between November 2008 and September 2009, the total intake of arsenic by the villagers correlated with the amount of water and local produce consumed.

The central portion of Argentina is affected by arsenic-contaminated groundwater. Specifically, the La Pampa produces water containing 4–5300 microgram per liter.

Arsenic contamination of the groundwater in Bangladesh is a serious problem. Prior to the 1970s, Bangladesh had one of the highest infant mortality rates in the world. Ineffective water purification and sewage systems, as well as periodic monsoons and flooding, exacerbated these problems. As a solution, UNICEF and the World Bank advocated the use of wells to tap into deeper groundwater. During the 1970s, UNICEF worked with the Department of Public Health Engineering to install tube-wells. The wells consist of tubes 5 cm in diameter inserted less than 200 m into the ground and capped with an iron or steel hand pump. At that time, standard water testing procedures did not include arsenic testing. This lack of precaution led to one of the largest mass poisonings of a population because the ground water used for drinking was contaminated with arsenic.