The tradition of storing drinking water in copper vessels has been practiced for centuries, particularly in systems like Ayurveda, with the belief that the metal imparts beneficial properties to the water. This ancient practice has re-emerged recently through the popularity of copper cups and bottles. The core question is whether this tradition offers verifiable scientific benefits or presents safety concerns. Investigating this involves looking closely at copper’s role in human biology and how the metal interacts with water chemistry.
Copper’s Role as an Essential Nutrient
Copper is an essential trace mineral that the human body requires in small amounts to function properly. Once consumed, copper acts as a cofactor for several enzymes, playing a part in energy production and the formation of connective tissues. It is also necessary for the proper absorption and metabolism of iron, helping in the creation of red blood cells.
The mineral supports immune function and acts as an antioxidant component, specifically within the enzyme superoxide dismutase, which helps dismantle free radicals. The Recommended Dietary Allowance (RDA) for adult men and women is 900 micrograms (\(\mu\)g) daily, which most people easily meet through a balanced diet rich in foods like nuts, seeds, and shellfish. Consuming water that has been in contact with copper can contribute to this daily requirement.
How Copper Leaches into Stored Water
The process by which copper enters the water from the vessel is known as leaching, where copper ions (\(\text{Cu}^{2+}\)) dissolve from the metal’s surface into the liquid. The amount of copper released depends on several factors, including the duration of storage, the water’s temperature, and its acidity (pH level). Leaching increases significantly when water is left in the vessel for longer periods, such as overnight.
In studies using neutral drinking water, the copper concentration after 16 hours of storage was found to be very low, approximately \(0.177\) milligrams per liter (mg/L). This trace amount is considered well within safe limits for consumption set by major health organizations. However, the presence of acid dramatically accelerates this process, with acidic liquids like citrus juice leaching extremely high concentrations. For this reason, acidic beverages should never be stored in unlined copper cups or containers.
Evaluating Copper’s Antimicrobial Effects
The primary scientific claim supporting the use of copper vessels relates to the metal’s proven ability to kill microorganisms, a phenomenon called the oligodynamic effect. This effect refers to the toxic action of minute concentrations of heavy metal ions on bacteria, algae, and fungi. Studies have demonstrated that storing contaminated water in copper vessels can effectively purify it by eliminating common waterborne pathogens.
Copper ions achieve this by damaging the cell walls and proteins of bacteria, which leads to their inactivation and death. Research has shown that copper pots can achieve a complete reduction of microbial load for bacteria such as E. coli, Vibrio cholerae, and Salmonella typhi. This purification effect typically requires the water to be stored in the vessel for a sufficient contact time, often reported as 16 to 24 hours.
Safety Concerns and Defining Toxic Limits
While copper is required for health, excessive intake can lead to copper toxicity. The body efficiently regulates copper levels, but consuming too much can overwhelm its natural excretion processes. The Tolerable Upper Intake Level (UL) for adults is set at 10,000 \(\mu\)g (or 10 mg) per day.
Exceeding this limit can cause symptoms ranging from acute digestive distress to more serious long-term issues. Common symptoms of acute copper poisoning include nausea, vomiting, abdominal pain, and diarrhea. In severe or chronic cases, excessive copper can lead to liver damage. The risk of toxicity is highest when storing acidic liquids in the copper vessel or when consuming water from corroded or improperly lined vessels.