The public water supply in the United States is regulated to be potable upon delivery, but drinking water from the bathroom tap is generally not recommended. This difference stems from the water quality delivered to the home versus the quality after it has traveled through the internal residential plumbing system. While cold water from the bathroom faucet is typically safe, the warm water side presents specific risks related to materials and storage conditions. Experts advise using only cold water from a consumption source, like the kitchen tap, for drinking and cooking.
Understanding Residential Plumbing: Cold vs. Hot Water Lines
The cold water line in a home is a direct feed, carrying water straight from the municipal supply line to the fixture. This water has minimal contact time with the home’s internal plumbing and is maintained at a cool temperature. The cold water side of a bathroom faucet is generally considered the same quality as the kitchen tap, provided the pipes are not heavily used or corroded.
The hot water line follows a different path, leading to a storage tank or heating unit. Water remains in the heater for extended periods, introducing stagnation and temperature fluctuation. This storage process changes the water’s chemical and biological profile compared to the fresh, cold supply.
Hot water systems often use materials not intended for drinking water quality standards. Tanks are designed for washing and heating, not for preserving potable water quality. The prolonged time allows sediment or dissolved material to accumulate, which is then delivered through the hot water tap. This difference is why cold water is the preferred choice for consumption.
Specific Risks of Drinking Bathroom Tap Water
Heating and storing water significantly increases the potential for heavy metal leaching from plumbing materials. Hot water is a more aggressive solvent than cold water, dissolving metals like lead and copper from older pipes, solder, and brass fixtures at an accelerated rate. Even modern “lead-free” brass fixtures contain a small percentage of lead, which hot water can cause to leach out.
This chemical process is relevant in older homes where copper pipes were joined with lead-based solder, or where the main service line is made of lead. Metal concentration relates directly to how long the water has been sitting and its temperature. Heating water can also increase the concentration of disinfection byproducts (DBPs), such as trihalomethanes (TTHMs), formed when chlorine reacts with organic matter.
A significant biological risk is the potential for bacterial growth, particularly Legionella species, which cause Legionnaires’ disease. These bacteria thrive in warm, stagnant water, especially if the hot water tank is set below 140°F (60°C). Lower temperatures, sometimes used to prevent scalding, create an environment where bacteria can proliferate inside the tank and warm water lines. The presence of these organisms indicates a compromise in water quality due to the hot water system.
Regulatory Safety Standards in the United States
The safety of public water in the U.S. is overseen by the Environmental Protection Agency (EPA) through the Safe Drinking Water Act (SDWA). This federal law mandates that public water systems test and treat water to meet national health-based standards for contaminants. Water leaving the municipal treatment plant is rigorously monitored to ensure it is safe and potable.
The EPA’s regulatory jurisdiction typically ends at the service line or water meter connecting the public system to private property. The utility is responsible for the quality of the water delivered to the home, but the homeowner is responsible for the quality once it enters their internal plumbing. The SDWA provides a strong foundation for water safety up to the point of entry.
The Lead and Copper Rule, part of the SDWA, manages the risk of metal leaching by requiring water systems to control the corrosivity of the water they deliver. Despite these measures, the final quality of the water at the tap depends heavily on the age and condition of the residential plumbing materials. The water’s journey through private pipes, particularly the hot water system, introduces variables not covered by public regulatory testing.