The increasing visibility of water packaged in aluminum cans reflects a growing consumer movement away from single-use plastic bottles. This shift is largely driven by aluminum’s high recyclability rate and a perception of greater environmental sustainability compared to PET plastic. As this packaging option becomes common, consumers question the safety of storing drinking water in metal containers. Concerns center on whether the aluminum itself or the materials used to protect the water introduce unwanted substances. This article examines the scientific and regulatory factors that determine the safety and quality of water in aluminum cans.
The Essential Internal Liner
Aluminum is a reactive metal that would rapidly corrode when exposed to water, especially acidic water. This reaction would compromise the can’s structural integrity and cause the water to acquire an unpleasant metallic flavor. To prevent this, every aluminum can is engineered with an ultra-thin polymer coating, or “lacquer,” sprayed onto the interior surface.
This coating functions as a physical, inert barrier, ensuring the water never makes direct contact with the metal. The liner prevents the water and container from forming a galvanic cell, which drives corrosion. Liners are typically made from plastic-based materials, such as epoxy resins, acrylics, or vinyl compounds, and are about 1 to 10 microns thick. The liner’s ability to adhere tightly to the metal and withstand internal pressure maintains the safety and quality of the canned water.
Specific Chemical Safety Concerns
The most significant public health discussion regarding canned beverages focused on Bisphenol A (BPA), which was a common component in older epoxy can linings. BPA is classified as an endocrine disruptor because it can mimic hormones, causing consumer concern about its potential health effects, even at low levels of exposure. Despite regulatory assurances that migration levels were safe, consumer demand prompted manufacturers to switch to “BPA-free” linings.
Replacement compounds, such as Bisphenol S (BPS) and Bisphenol F (BPF), are now widely used. Since these substitutes are structurally similar to BPA, some scientists caution they may possess comparable endocrine-disrupting properties. This raises questions about whether the switch represents a true safety improvement or merely a “regrettable substitution.”
Concerns about the leaching of aluminum or heavy metals are mitigated by the internal polymer barrier. The liner creates a zero-contact environment that prevents the transfer of metal ions into the water. Scientific evidence suggests that aluminum levels in canned water are well within established safe limits, provided the can’s lining remains intact.
Regulatory Oversight and Consumer Confidence
The materials used in aluminum can linings are categorized as indirect food additives and are subject to stringent control by government agencies, such as the U.S. Food and Drug Administration (FDA). These regulations are governed by the Federal Food, Drug, and Cosmetic Act (FFDCA), which ensures that food contact substances are safe for their intended use.
Regulators establish strict migration limits specifying the maximum allowed amount of any substance that can transfer from the packaging into the beverage. Compliance is demonstrated through migration testing, where the concentration of extractives is measured against these set limits. Substances migrating below 0.5 parts per billion (ppb) may receive a Threshold of Regulation (TOR) exemption if they are not carcinogenic and do not impact the food’s quality. This regulatory framework requires manufacturers to demonstrate the safety of can linings before they enter the market, fostering consumer trust that the packaging is continuously monitored and tested.
Effects on Water Quality and Taste
The aluminum can structure offers distinct advantages for preserving the sensory qualities of the water. Unlike plastic bottles, aluminum cans provide a complete barrier to oxygen and light, factors that degrade water quality over time. By blocking these elements, the packaging helps maintain the water’s fresh taste and prevents the formation of off-flavors common in other containers.
The internal lining plays a direct role in taste by eliminating metallic flavor transfer. If the polymer lining is intact, the water is insulated from the aluminum, and the consumer should not detect a metallic taste. A noticeable metallic taste indicates a compromised liner, which may result from manufacturing defects or physical damage to the can. The liner thus ensures chemical safety while preserving the water’s intended neutral flavor profile.