The question of whether it is safe to drink hot water straight from the tap is common, often driven by a desire for convenience. The definitive answer from health and plumbing experts is a clear no. Hot tap water should not be used for drinking, cooking, or making baby formula because the heating process and the storage environment introduce chemical and biological risks not present in cold tap water.
Why Hot Water Magnifies Contaminant Leaching
Heating water significantly increases the rate at which metallic compounds are dissolved from your home’s plumbing infrastructure. This chemical process, known as leaching, is accelerated by higher temperatures, which make the water more corrosive to metal pipes and fixtures. The longer water sits hot inside the plumbing system, the greater the concentration of these dissolved materials becomes.
Older homes often contain plumbing components that can leach heavy metals, such as lead from service lines or solder, and copper from pipes. Hot water also erodes the protective mineral scale, or patina, that naturally forms on the inside of pipes, exposing fresh metal. High concentrations of these metals can be harmful; lead is a potent neurotoxin, and excess copper can cause gastrointestinal distress.
The Hidden Risks in Hot Water Storage Tanks
A distinct biological risk is introduced within the hot water heater or storage tank itself. These tanks accumulate sediment, a mixture of rust and minerals, settling at the bottom. This layer of sediment acts as a nutrient source and a protective habitat for bacteria.
The primary concern is the growth of Legionella bacteria, the organism responsible for Legionnaires’ disease. This pathogen thrives in stagnant, warm water environments, with optimal growth occurring between 77°F and 113°F (25°C to 45°C).
Many residential hot water heaters are set to 120°F (49°C) to prevent scalding. This temperature is warm enough to promote bacterial survival but not hot enough to consistently kill the bacteria. Health organizations recommend storing water above 140°F (60°C) to ensure the bacteria are killed, but this high temperature creates an immediate scalding hazard at the tap.
Practical Guidelines for Safe Tap Water Use
The most straightforward guideline is to always draw water from the cold tap for any purpose involving consumption. Cold water bypasses the storage tank entirely, coming directly from the main supply line. This water is less likely to have corrosive effects on the plumbing. If hot water is needed for cooking or beverages, draw cold water and heat it separately in a kettle or on the stove.
It is also recommended to “flush” the cold water line before consuming it, especially first thing in the morning or after the water has been sitting unused. Running the cold water for 30 to 60 seconds clears the stagnant water resting in your home’s internal pipes. If your home has a lead service line or older plumbing, running the cold water for three to five minutes may be necessary to reduce potential contaminant levels.