Lead contamination in household water supplies is a significant concern because lead is a toxic heavy metal with no known safe exposure level, particularly for children. Exposure to lead can cause serious health issues, including damage to the nervous system and developmental problems. The metal typically enters drinking water through corrosion of plumbing materials like lead pipes, solder, and brass fixtures, especially in older homes.
The Chemistry of Boiling Water and Lead Concentration
Boiling water does not remove lead; in fact, the process increases the concentration of lead in the remaining water. This is due to the vast difference in boiling points: water boils at 100°C (212°F), while lead boils at approximately 1749°C (3180°F).
When water is heated, pure water molecules evaporate as steam, but dissolved solids and heavy metals, including lead, are non-volatile and remain behind. As the water volume decreases through evaporation, the lead concentration relative to the remaining water volume becomes higher. If you boil water until half of it has evaporated, the concentration of lead will nearly double, making the water residue more harmful than the original tap water.
What Boiling Water Actually Removes
Boiling water is an effective method for removing biological pathogens. The heat from a rolling boil is sufficient to kill or inactivate common waterborne microorganisms, including bacteria, viruses, and protozoa. This is why public health officials issue “boil water” advisories when the water supply is compromised by a biological threat.
Boiling can also reduce temporary water hardness, which is caused by dissolved calcium and magnesium bicarbonates. When boiled, these minerals precipitate out of the water as solid scale. Boiling water is a method of disinfection, targeting biological contaminants, not a method of purification, which targets chemical contaminants like lead.
Effective Strategies for Removing Lead from Drinking Water
Since boiling is ineffective, the most reliable approach for lead removal involves certified filtration methods. Before investing in a system, a water test should be conducted to determine the actual lead concentration in both “first draw” (stagnant) and “flushed” water samples.
Certified Filtration
One common and accessible method is using filters certified to meet the NSF/ANSI Standard 53. This standard confirms a product’s ability to reduce lead to a safe level, typically below 5 parts per billion (ppb), which is significantly lower than the EPA’s action level of 15 ppb. These filters often use granular activated carbon (GAC) or carbon block technology, removing lead through physical filtration and chemical adsorption.
Reverse Osmosis (RO)
RO systems offer a higher level of protection by using pressure to force water through a semi-permeable membrane. The membrane physically blocks nearly all dissolved solids, including heavy metal ions like lead, making RO systems highly effective. While more expensive and slower than standard carbon filters, RO units produce water with very low levels of contaminants.
Distillation
Distillation is a third highly effective technique that mimics the natural water cycle. The process involves boiling the water to create pure steam, which is then collected and condensed back into liquid form in a separate container. Since lead cannot evaporate with the water, it is left behind in the boiling vessel, resulting in water that is virtually free of all non-volatile solids.