# Is water from hot tap safe to drink? **URL:** \ **Category:** Factual Questions\ **Created:** [November 16, 2003, 6:15pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568 "2003-11-16T18:15:30Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Weatherman\_Skye\_Forrest](https://avatars.discourse-cdn.com/v4/letter/w/dec6dc/32.png) [@Weatherman\_Skye\_Forrest](https://boards.straightdope.com/u/Weatherman_Skye_Forrest)\ **Post date:** [November 16, 2003, 6:15pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/1 "2003-11-16T18:15:30Z")
Instructions for coffee, tea, oatmeal, etc. often specify you start with cold water and then heat to boiling. Isn’t the hot water the same, only hotter? Unless your hot water tastes of iron (which can happen in the cold pipes as well), what’s the dif? ---
**Author:** ![Coffeeguy](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@Coffeeguy](https://boards.straightdope.com/u/Coffeeguy)\ **Post date:** [November 16, 2003, 6:37pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/2 "2003-11-16T18:37:07Z")
It will kill you. ---
**Author:** ![Matchka](https://avatars.discourse-cdn.com/v4/letter/m/77aa72/32.png) [@Matchka](https://boards.straightdope.com/u/Matchka)\ **Post date:** [November 16, 2003, 6:40pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/3 "2003-11-16T18:40:05Z")
The diff is that the hot water tank gets a little gunky. Water from it can bring forth to you some of that gunk and is not as nice :hurk: as the fresh tap water provided by the city. :bllleeeeeeeaaaaahhhhhh!: :hurk: ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [November 16, 2003, 7:54pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/4 "2003-11-16T19:54:49Z")
Hot water might leach nasty things out of pipes and the solder faster than cold water does. Although lead isn’t used in plumber’s solder any more plenty of other things are. ---
**Author:** ![I\_can\_t\_believe\_that\_s\_butter](https://avatars.discourse-cdn.com/v4/letter/i/8edcca/32.png) [@I\_can\_t\_believe\_that\_s\_butter](https://boards.straightdope.com/u/I_can_t_believe_that_s_butter)\ **Post date:** [November 16, 2003, 8:12pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/5 "2003-11-16T20:12:55Z")
> [@](#): > > \*Originally posted by Coffeeguy \* > \*\*It will kill you. \*\* At the risk of dissecting the frog—cite? ---
**Author:** ![Weatherman\_Skye\_Forrest](https://avatars.discourse-cdn.com/v4/letter/w/dec6dc/32.png) [@Weatherman\_Skye\_Forrest](https://boards.straightdope.com/u/Weatherman_Skye_Forrest)\ **Post date:** [November 16, 2003, 8:48pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/6 "2003-11-16T20:48:52Z")
Sludge? My water heater has a sludge spigot, but whenever I’ve drained it (before working on the other pipes) it runs clear. It’s glass-lined, after all. ---
**Author:** ![Ferret\_Herder](https://avatars.discourse-cdn.com/v4/letter/f/e47774/32.png) [@Ferret\_Herder](https://boards.straightdope.com/u/Ferret_Herder)\ **Post date:** [November 16, 2003, 8:56pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/7 "2003-11-16T20:56:49Z")
What I’ve always been told is that hot water can have chemicals in it from your water softener. Cold water is not softened. Softened water is supposed to convey a salty taste to food. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 16, 2003, 9:08pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/8 "2003-11-16T21:08:00Z")
> [@](#): > > Softened water is supposed to convey a salty taste to food. That’s because water softeners work by exchanging salt for all the other ions _e.g._ iron, selenium, mercury, lead, sulphates, tannins _etc._ that are present in your cold water supply. ---
**Author:** ![gentle](https://avatars.discourse-cdn.com/v4/letter/g/eb8c5e/32.png) [@gentle](https://boards.straightdope.com/u/gentle)\ **Post date:** [November 16, 2003, 9:25pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/9 "2003-11-16T21:25:58Z")
I’ve always been told to use cold water for cooking if the building has an older plumbing system that uses copper pipes. Copper poisoning is apparently a very real risk. My apartment building is barely 10 years old, but the plumbing seems to be all copper, based on the apparent verdigris (ie., copper sulfate) deposits that accumulates in my sink and in the shower. Also, what the other posters said. ---
**Author:** ![Coffeeguy](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@Coffeeguy](https://boards.straightdope.com/u/Coffeeguy)\ **Post date:** [November 16, 2003, 9:29pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/10 "2003-11-16T21:29:07Z")
If your water has any alkalinity at all, you’ll be more interested in learning the solubility of the metal carbonate salts rather than the metal it’s self since that’s how the metals will go into solution. Even so, with water 60C warmer sitting in your pipes, you might double or triple the metal’s solubility in the water. The next thing you’d want to know is do you have lead pipes? Where I live they don’t exist anymore, and even copper is on it’s way out. If you do have lead pipes you shouldn’t really be drinking any water flowing through them; worrying about how much more lead gets into the hot water from the tiney amount of contact time and length of unsuitable piping is sort of like worrying about whether you smoke light vs regular cigarettes - you’re screwed either way. The amounts of dangerous metals in proper piping are only present in trace amounts anyways, which shouldn’t be dangerous… there’s more potential for your water supply to have bad water at the source (which is regulated) than for it to become dangerously contaminated flowing through 15 feet of pipe for a few seconds. And once again the scale you see in water tanks (mostly from calcium bicarbonate) has been precipitated out of your water during heating, hence this water has less of these minerals in it when it comes out the tap. And the reason it precipitates out is that the water cannot hold more than a certain amount of these minerals at the temperature it gets heated too, so it’s not gonna pick up any extra when it flows through the heater tank. If your water is depositing minerals already, it’s not going to pick up any more even if you dumped 50 pounds of it into the tank. Not to mention that calcium/magnesium carbonates and bicarbonates aren’t going to hurt you anyways. For that matter, neither will copper or iron in the amounts leached into a few feet of pipe - people purposely take all kinds of metal supplements daily. And to be picky, there will be one hell of a lot more metals leaching out of your pot or pan once you start frying or boiling at the really high temperatures than will come out of your water pipes at relatively low temperatures… and then we go scrubbing those metal pots nice and good afterwords to expose more new metal for the water to suck out next time, leave a bit of soap residue on them, and so on… Lastly I measured the flow rate of my kitchen sink and the length of pipe between it and the water heater. There are about 15 feet of 1/2" copper pipe between the two, which holds a volume of 0.6L. The flow rate is 12L/minute. I also timed how long it took for the water coming out of the hot tap to “get hot” - 15 seconds. So, at a flow of 12LPM, it takes 3.2 seconds for the entire volume of the heater-to-sink hot water pipe to clear, and by the time the water is hot enough for me to stick the pot underneath it, that volume has been replaced almost five times. The water going into my pot has a total exposure time of 5 seconds at 60-70C in those copper pipes. The metals that would have leached into it overnight are long gone before I even grab a pot to fill. Disolved gases like chlorine will come out of solution faster from heated water, which most would consider good; even so the chlorine concentration is too low to be dangerous. Most of the bacteria that are human pathogens are mesophilic, dying off at temps above 45C… the thermophilic bacteria that may be in your water heater, if not already dead from the cold initial temps and chlorine throughout their stay, don’t seem to be a problem either. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [November 16, 2003, 11:34pm UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/11 "2003-11-16T23:34:13Z")
Hmmm, that post sounds [familiar](http://boards.straightdope.com/sdmb/showthread.php?threadid=156449) for some reason… 🆒 ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2003, 12:41am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/12 "2003-11-17T00:41:46Z")
Some hot water systems (at least in this country) have a header tank in the roof space and this is often not securely covered; bugs, birds and dirt can fall into it, contaminating the water. ---
**Author:** ![Coffeeguy](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@Coffeeguy](https://boards.straightdope.com/u/Coffeeguy)\ **Post date:** [November 17, 2003, 1:06am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/13 "2003-11-17T01:06:46Z")
Dratted missing "Quoted from the amazing **mmmiiikkkeee**"tags! ---
**Author:** ![Weatherman\_Skye\_Forrest](https://avatars.discourse-cdn.com/v4/letter/w/dec6dc/32.png) [@Weatherman\_Skye\_Forrest](https://boards.straightdope.com/u/Weatherman_Skye_Forrest)\ **Post date:** [November 17, 2003, 1:32am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/14 "2003-11-17T01:32:00Z")
> [@](#): > > \*Originally posted by Mangetout \* > \*\*Some hot water systems (at least in this country) have a header tank in the roof space and this is often not securely covered; bugs, birds and dirt can fall into it, contaminating the water. \*\* This would be useful information if more people lived, like you do in “Location: The Kingdom of Butter” 😃 ---
**Author:** ![Wheel](https://avatars.discourse-cdn.com/v4/letter/w/4da419/32.png) [@Wheel](https://boards.straightdope.com/u/Wheel)\ **Post date:** [November 17, 2003, 1:39am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/15 "2003-11-17T01:39:17Z")
Ok, here’s the straight dope on this. The water that goes into your heater is the same water that comes out your cold tap. The danger is this, the heater elements can deteriorate and contaminate the water to a certain extent. In fact, since most modern electric hot water heaters use 2 elements one can be broken completely in two and the other will still be heating the water. In short, no,don’t drink the hot water from the electric hot water heater. It can be contaminated by the heaters. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [November 17, 2003, 1:44am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/16 "2003-11-17T01:44:04Z")
> [@](#): > > \*Originally posted by Coffeeguy \* > \*\*If your water has any alkalinity at all, you’ll be more interested in learning the solubility of the metal carbonate salts rather than the metal it’s self since that’s how the metals will go into solution. Even so, with water 60C warmer sitting in your pipes, you might double or triple the metal’s solubility in the water. The next thing you’d want to know is do you have lead pipes? Where I live they don’t exist anymore, and even copper is on it’s way out. If you do have lead pipes you shouldn’t really be drinking any water flowing through them; worrying about how much more lead gets into the hot water from the tiney amount of contact time and length of unsuitable piping is sort of like worrying about whether you smoke light vs regular cigarettes - you’re screwed either way. > > The amounts of dangerous metals in proper piping are only present in trace amounts anyways, which shouldn’t be dangerous… there’s more potential for your water supply to have bad water at the source (which is regulated) than for it to become dangerously contaminated flowing through 15 feet of pipe for a few seconds. > > And once again the scale you see in water tanks (mostly from calcium bicarbonate) has been precipitated out of your water during heating, hence this water has less of these minerals in it when it comes out the tap. And the reason it precipitates out is that the water cannot hold more than a certain amount of these minerals at the temperature it gets heated too, so it’s not gonna pick up any extra when it flows through the heater tank. If your water is depositing minerals already, it’s not going to pick up any more even if you dumped 50 pounds of it into the tank. Not to mention that calcium/magnesium carbonates and bicarbonates aren’t going to hurt you anyways. > > For that matter, neither will copper or iron in the amounts leached into a few feet of pipe - people purposely take all kinds of metal supplements daily. And to be picky, there will be one hell of a lot more metals leaching out of your pot or pan once you start frying or boiling at the really high temperatures than will come out of your water pipes at relatively low temperatures… and then we go scrubbing those metal pots nice and good afterwords to expose more new metal for the water to suck out next time, leave a bit of soap residue on them, and so on… > > Lastly I measured the flow rate of my kitchen sink and the length of pipe between it and the water heater. There are about 15 feet of 1/2" copper pipe between the two, which holds a volume of 0.6L. The flow rate is 12L/minute. I also timed how long it took for the water coming out of the hot tap to “get hot” - 15 seconds. > > So, at a flow of 12LPM, it takes 3.2 seconds for the entire volume of the heater-to-sink hot water pipe to clear, and by the time the water is hot enough for me to stick the pot underneath it, that volume has been replaced almost five times. The water going into my pot has a total exposure time of 5 seconds at 60-70C in those copper pipes. The metals that would have leached into it overnight are long gone before I even grab a pot to fill. > > Disolved gases like chlorine will come out of solution faster from heated water, which most would consider good; even so the chlorine concentration is too low to be dangerous. Most of the bacteria that are human pathogens are mesophilic, dying off at temps above 45C… the thermophilic bacteria that may be in your water heater, if not already dead from the cold initial temps and chlorine throughout their stay, don’t seem to be a problem either. \*\* OK, _you_ go ahead and use it then. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 17, 2003, 1:46am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/17 "2003-11-17T01:46:33Z")
> [@](#): > > \*Originally posted by Weatherman Skye Forrest \* > \*\*This would be useful information if more people lived, like you do in “Location: The Kingdom of Butter” 😃 \*\* Good point; I sometimes wonder though, if people are sick of me saying “here in the UK…” (or perceive it in the wrong kind of light). Perhaps I should just be subtle and drop in an occasional reference to steak and kidney pies. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [November 17, 2003, 3:15am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/18 "2003-11-17T03:15:01Z")
“Don’t drink the hot water!” is just unscientific panic. If you have lead pipes, don’t drink the hot or cold water. The rest is just fine. As I pointed out in the earlier thread, a hot water tank acts as a settling tank so there is actually _less_ sediment in hot water. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [November 17, 2003, 3:26am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/19 "2003-11-17T03:26:11Z")
> [@](#): > > OK, _you_ go ahead and use it then. I’m 26 years ahead of ya there, pal 😉 . ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [November 17, 2003, 3:33am UTC](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568/20 "2003-11-17T03:33:37Z")
> [@](#): > > \*Originally posted by David Simmons \* > \*\*OK, _you_ go ahead and use it then. \*\* I do all the time. Have done for 37 years. _That_ explains why I’m balding and feel more tired than when I was 16. Damned hot tap water… [Next page](https://boards.straightdope.com/t/is-water-from-hot-tap-safe-to-drink/213568.md?page=2)