Boiling water is a widely practiced method for making water safer to drink, but it is entirely ineffective for removing heavy metals. Heating water to its boiling point does not eliminate contaminants like lead, arsenic, or mercury. In fact, boiling water can increase the concentration of these harmful substances in the remaining liquid, potentially making the water more dangerous to consume.
Why Boiling Fails to Remove Heavy Metals
Heavy metals exist in water as dissolved solids, specifically as metal ions. When water is heated, the liquid water turns into steam, which is the gaseous form of pure \(\text{H}_2\text{O}\). Heavy metals have extremely high boiling points, far exceeding the \(100^{\circ}\text{C}\) (212°F) temperature at which water boils at sea level. Because these metal ions are non-volatile, they do not evaporate with the water vapor and remain in the boiling vessel. For example, lead remains fully soluble in the hot water throughout the boiling process.
The most concerning outcome is the resulting concentration effect. As the water volume decreases due to evaporation, the mass of the heavy metal contaminant stays the same. This increases the ratio of heavy metal to water, causing the concentration (measured in parts per million) to rise in the residual water. Studies have shown that boiling water can elevate the concentration of lead by 10% or more, depending on how much water is lost to steam.
Contaminants Boiling Effectively Eliminates
The widespread belief that boiling purifies water stems from its effectiveness against biological threats. Boiling is a powerful method for eliminating pathogenic microorganisms that cause waterborne illnesses, including bacteria, viruses, and protozoan cysts such as E. coli, Salmonella, and Giardia.
The intense heat denatures the proteins and destroys the structure of these organisms, preventing them from reproducing. Maintaining a rolling boil for one to three minutes is sufficient to make biologically contaminated water safe to drink. This method is useful in emergency situations or when sourcing water from untreated supplies.
Boiling can also remove some volatile chemical compounds, such as chlorine, which is often added to municipal water supplies as a disinfectant. The heat causes the chlorine to convert to a gas and escape from the water, improving the taste and odor. Additionally, the process removes dissolved gases like oxygen and carbon dioxide, which gives boiled water its characteristically flat taste.
Proven Technologies for Removing Heavy Metals
Since boiling is ineffective for heavy metals, specialized filtration and purification technologies are necessary to achieve safe drinking water.
Reverse Osmosis (RO)
Reverse Osmosis (\(\text{RO}\)) forces water under pressure through a semi-permeable membrane. This membrane has pores small enough to block dissolved inorganic contaminants, including heavy metal ions like lead, arsenic, and chromium, removing up to 99% of these substances.
Distillation
Distillation mimics boiling but collects the resulting pure water vapor. Water is boiled to create steam, leaving all non-volatile solids and metals behind. The steam is then condensed back into purified liquid water. Distillation can remove nearly all contaminants, including heavy metals, but it is an energy-intensive and slow process.
Ion Exchange
Ion exchange uses specialized synthetic resins to capture specific metal ions. As contaminated water passes through the resin, heavy metal ions (such as copper or lead) are chemically swapped for harmless ions like sodium or hydrogen. This method is highly efficient for targeted metals but requires periodic regeneration of the resin to maintain effectiveness.
Activated Carbon Filters
Standard activated carbon filters are designed to remove organic compounds, not heavy metals. However, specialized variations can be employed. Activated carbon combined with specific media enhancements, such as \(\text{KDF}\) (Kinetic Degradation Fluxion), can improve the removal of certain heavy metals like lead. For comprehensive heavy metal removal, a multi-stage filtration system incorporating an \(\text{RO}\) membrane combined with ion exchange or specialized carbon is the most reliable choice.