Aluminum is the most abundant metallic element found in the Earth’s crust, making its presence in the environment, including water sources, entirely natural. It exists primarily within rocks and soil as oxides and silicates. When water contacts these geological formations, small amounts of aluminum dissolve into the water supply. Understanding the sources and chemical behavior of this element addresses concerns about its safety in drinking water.
Sources of Aluminum in Drinking Water
Aluminum enters the water supply through a combination of natural processes and human activities, leading to varying concentrations in different regions. The most fundamental source is the natural weathering of aluminum-rich minerals, such as feldspar, in the earth’s crust. As surface water flows over rocks and soil, the element dissolves and is carried into reservoirs and aquifers.
A significant source of aluminum is its use in municipal water treatment facilities. Treatment plants frequently add aluminum compounds, most commonly aluminum sulfate (alum), to the water. This compound acts as a coagulant, binding tiny particles of matter, clay, and microorganisms so they can settle out or be filtered. While the goal is to remove these clumps, trace residual amounts can sometimes remain in the finished drinking water.
Aluminum can also enter drinking water after it leaves the treatment plant through leaching within the distribution system and the home. Corrosive water sitting in household plumbing can dissolve small amounts of metal from internal components. Additionally, unlined aluminum cookware or beverage containers can transfer the element to water when used for boiling or storage.
Factors Governing Aluminum Leaching
The amount of aluminum that dissolves into water is governed by specific chemical and environmental conditions. The most influential factor is the water’s pH, which measures its acidity or alkalinity. Aluminum is an amphoteric substance, meaning it dissolves readily at both extremes of the pH scale.
Aluminum is at its least soluble when the water is near neutral, typically in the pH range of 6.5 to 7.5. However, if the water becomes highly acidic (low pH) or highly alkaline (high pH), the aluminum oxide protective layer on surfaces like pipes or cookware rapidly breaks down. For example, boiling water with acidic ingredients like vinegar or lemon juice in an unlined aluminum pot will significantly increase the amount of aluminum dissolved.
Temperature also plays a direct role in the rate of aluminum leaching. Higher temperatures increase the chemical reaction speed, causing more aluminum to dissolve from contact surfaces, such as cookware or water heater components. Furthermore, the duration of contact is important; stagnant water sitting in pipes or a kettle will accumulate a higher concentration of dissolved aluminum than fresh, flowing water.
Health Effects of Aluminum Consumption
The human body is efficient at managing the low levels of aluminum ingested through food and drinking water. Only a small fraction (typically 0.01% to 5%) of orally ingested aluminum is absorbed by the digestive tract. The majority of the absorbed aluminum is rapidly processed and excreted by the kidneys through urine.
Regulatory bodies establish limits to protect public health. The U.S. Environmental Protection Agency (EPA) has set a Secondary Maximum Contaminant Level (SMCL) for aluminum in drinking water at 0.05 to 0.2 milligrams per liter (mg/L). This standard is not based on a direct health risk for the general population but is a guideline to prevent aesthetic issues like water discoloration or sediment buildup.
Concerns about aluminum toxicity are generally limited to specific, vulnerable populations. Individuals with severe kidney impairment, particularly those undergoing dialysis, cannot effectively excrete aluminum, leading to accumulation that may cause neurological or bone issues. Scientific consensus holds that evidence for a causal relationship between aluminum in water and neurodegenerative conditions at typical consumption levels is inconclusive or weak.
Reducing Aluminum Exposure in the Home
For those concerned about aluminum levels, several steps can minimize exposure. The first step for anyone on a private well or who suspects high concentrations is to have the water tested, as this is the only way to confirm the actual level of aluminum present.
Water filtration offers an effective method for removal, with Reverse Osmosis (RO) systems being highly capable. An RO system forces water through a semi-permeable membrane, which has been shown to reduce aluminum content by a significant margin. While less effective, some specialized filters containing activated alumina or other adsorption media can also help reduce concentrations.
Simple adjustments to household habits can also reduce exposure from internal plumbing. Allowing the cold water tap to run for 30 seconds to one minute flushes out water that has been sitting in the pipes and accumulating leached metals. When using aluminum cookware, avoid cooking or storing highly acidic foods, such as tomato sauce, citrus juices, or rhubarb, as the low pH dramatically increases the rate of aluminum leaching.