Is it safe to drink hot tap water?
Executive summary
Hot tap water is routinely advised against for drinking, cooking, and making baby formula because heating and storage increase the risk that harmful metals and microbes will be present at higher levels than in cold tap water [1][2]. Public health agencies and water utilities therefore recommend using cold water for consumption, flushing taps, and relying on treated or tested sources to be safe [1][2][3].
1. Why federal and local agencies say “no” to hot-tap consumption
The U.S. Environmental Protection Agency’s clear guidance is that hot water dissolves lead more quickly than cold and that people should never use water from the hot tap for drinking, cooking, or making baby formula; that recommendation underpins many local advisories [1]. The Centers for Disease Control and Prevention also warns that hot water can dissolve copper from pipes more easily and recommends flushing taps before using water for consumption, reinforcing that hot water is a different risk pathway than water straight from the distribution system [2]. Utilities such as Denver Water echo these directives, telling customers to always start with cold water for boiling and to avoid filling pots from the hot tap [3].
2. How heating and household plumbing change water chemistry
Heating accelerates leaching and corrosion processes in plumbing materials, so metals like lead, copper, zinc and other elements can be present at higher concentrations in hot tap water than in cold water that has not sat or been heated in the home plumbing system [4][5]. Multiple sources explain that hot water may bypass filtration devices installed on cold lines and that storage in hot-water tanks or stagnant hot lines can concentrate contaminants introduced by older fittings, soldered joints or brass components [4][5][6]. That is the mechanistic basis for agency-level caution, not a claim that every home’s hot water is contaminated, but that the potential and mechanism are well-documented [1][2].
3. Microbial risks, storage temperatures, and special settings
Beyond metals, improperly maintained hot-water systems can create settings where bacteria persist or proliferate if storage temperatures are too low or disinfectant residuals dissipate; public-health guidance around boil-water advisories and aircraft water studies shows microbes become a particular concern when water is stored or when systems are stagnant [7][8]. Airlines’ onboard water systems, for example, can harbor microbial risks in tanks and plumbing, prompting researchers to advise avoiding tap water inflight unless bottled [8]. Local health authorities such as NSW Health likewise highlight that hot water stored or delivered at wrong temperatures can provide breeding grounds for bacteria [4].
4. Practical precautions that public agencies recommend
Agencies consistently recommend using only cold tap water for drinking, cooking, and especially for baby formula, running the cold tap for a short flush if the fixture has been unused for hours, and contacting local utilities or health departments if contamination is suspected [1][2][7]. Utilities frame this as a simple mitigation: start with cold water, flush lines, rely on tested or treated sources—and in settings with known infrastructure problems or advisories, follow boil-water or utility-specific instructions [3][7].
5. Nuance, scope and limitations of the guidance
The guidance is precautionary and targeted: it stems from well-understood chemistry and documented failures in distribution and household plumbing, but it does not mean every hot tap in every home is definitively contaminated; rather, regulators advise against using hot tap water because the process of heating and household storage consistently raises the risk profile compared with cold water drawn directly from the supply [1][2][9]. Where local water quality testing shows no exceedances and plumbing is modern and maintained, risks are lower—but the cited public-health stance remains conservative, especially for infants, pregnant people, and immunocompromised individuals [1][9].
6. Bottom line: is it safe?
For everyday, evidence-based decision-making, hot tap water should be treated as unsafe for drinking and cooking because heating and household plumbing commonly increase the chance of metal leaching and microbial issues; follow EPA, CDC and local utility guidance: use only cold water for consumption, flush lines that have been stagnant, and heed local advisories or testing results when available [1][2][3]. Where certainty is needed—making baby formula, serving immunocompromised people, or when infrastructure is old—the precaution is unambiguous: do not use hot tap water [1].