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February 3, 2008

BehindTheMedspeak: Don't drink the (hot) water


Anahad O'Connor's "Really?" column in the January 29, 2008 New York Times Science section asked if using hot tap water for drinking or cooking is safe.

Short answer: No.

Here's the column.

    The Claim: Never Drink Hot Water From the Tap

    The Facts: The claim has the ring of a myth. But environmental scientists say it is real.

    The reason is that hot water dissolves contaminants more quickly than cold water, and many pipes in homes contain lead that can leach into water. And lead can damage the brain and nervous system, especially in young children.

    Lead is rarely found in source water, but can enter it through corroded plumbing. The Environmental Protection Agency says that older homes are more likely to have lead pipes and fixtures, but that even newer plumbing advertised as “lead-free” can still contain as much as 8 percent lead. A study published in The Journal of Environmental Health in 2002 found that tap water represented 14 to 20 percent of total lead exposure.

    Scientists emphasize that the risk is small. But to minimize it, the E.P.A. says cold tap water should always be used for preparing baby formula, cooking and drinking. It also warns that boiling water does not remove lead but can actually increase its concentration. More information is at www.epa.gov/lead or (800) 424-5323 (LEAD).

    The Bottom Line: Hot water from the tap should never be used for cooking or drinking.


I was brought up to believe the above to be true, then when I went to college decided all old wives' tales were myths and that this was one so I started using hot tap water for cooking and tea and whatnot.

I stopped when I was an anesthesiology resident and met a nurse whose dad ran a plumbing business.

She told me that I should never use hot tap water for cooking or drinking, and that the reason was visible inside a water heater: she said they were coated with horrible gunk that, once seen, would put you off ingesting the contents for good.

So I ceased and desisted, then after a few years fell back into using hot tap water like I had when I was in college.

Then after I moved to Virginia my new neighbor told me that not only should I never use hot water for cooking or drinking, but that first thing in the morning I should run the cold water for a few minutes to wash out lead accumulated overnight in the standing water in the pipes.

So I did that for a few years, then went back to the quick and dirty of using hot tap water for coffee, tea and cooking.

Until last Tuesday, when I read O'Connor's column.

Now I'm back to the cold tap (without the priming) for probably the next few years.

I'm going to have my crack research team look a little deeper into this interesting topic; if they find anything of value you'll be the first to know.

February 3, 2008 at 04:01 PM | Permalink


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Thanks for the conflicting advice about drinking tap water. Even though my water heater is glass-lined and fairly new, the taste is still prohibitive. I've been very happy heating my water in the microwave. I've really been all over the internet trying to find out if tap water will hurt or kill my tropical fish. The volume I need for a water change is far too much to heat in the microwave. Anyone have an answer??

Posted by: Rich P. | Feb 11, 2008 11:57:35 PM

Interesting! I never use hot water from the tap, for a different but somewhat related reason. The cloudiness of it kind of grosses me out and makes me think there's something sketchy in it. I notice that when I heat tap water on the stove, it doesn't get very cloudy. I wonder what the difference is?

I've been a little reluctant to use tap water at all for the past couple of months, since the morning I woke up and it was coming out brown.

Posted by: Megan | Feb 6, 2008 11:19:51 AM

From Wikipedia:
Copper is an essential trace nutrient to all high plants and animals. In animals, including humans, it is found primarily in the bloodstream, as a co-factor in various enzymes, and in copper-based pigments. However, in sufficient amounts, copper can be poisonous and even fatal to organisms.

Cupric Chlorides (specifically Copper II Chloride) are formed by exposure to HCl. Once again, the introduction of HCl into the water mains can produce a standing body of water in your home that leaches Copper from the pipes. Dilution of metal salts by running the water is safer that using the steady-state/equilibrium reached by water that has been standing, under pressure, in your copper household water system.

One question that we have not addressed: what volume of water must pass through the system to dilute the standing cold water? In my home there is about 3 meters of pipe from the main to my kitchen and about 20 meters to the furthest bathroom. At 1 cm internal diameter I'd calculate 3 liters at the kitchen and 20 at the bath.

Simple solution - run the water in the sink before drinking - and use the toilet and take your shower (in that order, please, or we get into the f-o route of contamination) before brushing your teeth. 3000 Ml is less than a gallon at the kitchen sink.

Posted by: 6.02*10^23 | Feb 5, 2008 8:48:06 AM

I'll stick with the hot water from the tap for a lot of things. I have an instant/flash heater so there's no worry about all the gunk that I used to get in my old tank. The new supply pipe has only one solder joint between the heater and the kitchen tap and if you've ever seen a properly soldered joint cut in two then you'll know that the exposed area of lead (if any) is miniscule. If I were worried about that joint I'd change it to a compression fitting, but those can be a real pain.

Posted by: Graeme | Feb 4, 2008 11:42:16 PM

One more thing:
"minute risk of a little lead" is neither minute nor without serious risk.

See, Casarett & Doull's Toxicology: The Basic Science of Poisons ISBN-10: 0071347216

And, A Complete Guide to Lead Paint Poisoning Litigation ISBN-10: 157073562X

Posted by: 6.02*10^23 | Feb 4, 2008 7:21:32 PM

I have an "instant" water heater for tea, oatmeal, etc. It draws from the cold water system - and, yes - my house has copper pipe with soldered joints - so the cold runs for quite some time before I trigger the instant hot water.

This time of year a hand in the stream tells when I have "fresh" water - because the water inside the house is warmer that the water in the mains. Many times the opposite holds true in the summer. Fall and Spring you are on your own (unless you are obsessive enough to time the change and are willing to assume that the system pressure remains a constant.)

FWIW, I understand that from time to time, in "hard water" areas the water system administrators introduce a bolus of HCl at certain valves to prevent/remove CaCO3. I'd imagine that a few molecules of proton donor make it to our homes. Hmm, PbCO3 + 2 HCl → PbCl2 + CO2 + H2O - theoretically, insoluble - unless you add more HCl (like, say from a mammal's stomach?).

I've avoided hot water ever since my quant prof, dear old Dr. Ernst, had the class calculate how much distilled H2O would have to pass through a teakettle to remove 1gm/cm^2 of CaCO3. Let's just say that dihydrogen monoxide can carry far more solute the warmer it is up to 100c at which point it precipitates the solute and has a gas. A guy named Benoît Paul Émile Clapeyron wrote a bit about this back in 1834. He came up with PV=nRT based, in part, upon my namesake here's work: Avogadro's Principle.

Posted by: 6.02*10^23 | Feb 4, 2008 7:07:47 PM

I'm convinced, and will stop using hot water for my tea and cooking. However, I think running the cold water for a few minutes in the morning is not a good idea, sustainability-wise. Conserve resources and all that. How much energy does it take to render water potable? The more water you use, the more energy you use. I'd rather take the minute risk of a little lead in the water than contribute further to the cavalier use of resources in our society.

Posted by: Rena | Feb 4, 2008 12:10:39 PM

yea, I don't know about the lead issue, but I too stopped the hot water-for-cooking practice after seeing the inside of one of those things several years ago... nasty! an example pic halfway down:


Posted by: johnjohn | Feb 3, 2008 6:36:32 PM

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