Cold or warm water safest?

November 9, 2006 12:29 AM

Which is safest, hot or cold water from the tap?

My other half always uses cold water from the kitchen taps when cooking, washing food, and even brushing her teeth.

She maintains that this is because the hot water is usually stored at *warm*, not boiling temperatures, so becoming a much more effective breeding ground for germs than cold water.

Ignoring the practical benefits and the fact that cooking will kill most germs anyway, is she right, or can I frolic in warm water in safety?

posted by MintSauce to health (20 comments total)

She is right. Not only will you get germs in your hot water, which has been stagnating, but the hot water will also leech metals like copper or lead out of the pipe.
posted by grouse at 12:45 AM on November 9, 2006 [1 favorite]

The cold has more dissolved gasses however, you know, like chlorine. That's not so good.
posted by Pollomacho at 12:48 AM on November 9, 2006

It depends. There is a temperature at which health codes indicate hot water cylinder should be set above, above which bacteria die, below which, they don't. Some people save money by turning down the temp of the water cylinder, or never set it high enough in the first place (or maybe have it dift over the years as the device ages?). It comes down to whether your cylinder temperature is set correctly.

For what it's worth, I've never heard of anyone I know getting sick from hot water. (I know people who have turned the temp down too). I also subscribe to the theory that going too far to prevent your body from encountering a wide and constant range of bacteria and stuff just ends up making you more sickly, as your immune system ends up with a smaller, stunted library of antibodies to work from. Since I've never heard of anyone getting sick from hot water (though I know it can happen, as the basis for the temperature regulation is sound), I would put studiously avoiding it in the "probably does more harm than good" category, under the aforementioned theory :)
posted by -harlequin- at 1:07 AM on November 9, 2006

(I don't recall the health code safe temperature, but it is well below boiling point - the water isn't meant to be boiling in a hot water cylinder).
posted by -harlequin- at 1:12 AM on November 9, 2006

You just asked the right person, I am a water inspector and Grouse is right, never use your hot water out of the tap for cooking, you will have dissolved metals in your hot water heater.(plumbing soddering and whatnot) And always let your water run for a couple seconds before drinking it.
Why, trust me........
posted by highgene at 1:33 AM on November 9, 2006 [4 favorites]

Most of the dissolved metals in hot water actually come out of the sacrificial anode in the tank. Stainless steel tanks (as opposed to the much more common glass-lined mild steel tanks) don't need sacrificial anodes to stop them rusting out, so if you have one of those, the only thing you need to be worried about is lead-based solder joints in your plumbing. I live in a civilized country where plumbers use hard (silver-based) solder; your mileage may vary.
posted by flabdablet at 3:35 AM on November 9, 2006

I am a water inspector ....
posted by highgene

:)
posted by caddis at 3:50 AM on November 9, 2006

Cold water is better, as lead (from old pipes/solder) dissolves much more readily in warm water. Lead poisoning is cumulative, so anything you can do to avoid exposure to lead over the course of your lifetime is good.
posted by limeonaire at 5:36 AM on November 9, 2006

always let your water run for a couple seconds before drinking it.

I remember during a water shortage in NYC, I think it was Koch, doing a TV spot that said: "It's important to save water, but dont' neglect to let the water run for a full minute before drinking."

If you put your hand in the cold water stream you can usually feel two progressive drops in temperature as it runs: one when you get water from the building main, another when you get to water from the street main.

It's most important to clear that first batch of water, because those are the pipes that may have been installed by DIY plumbers like myself who slathered on the flux and lead solder.
posted by StickyCarpet at 6:02 AM on November 9, 2006

Yes, the germs are not the issue, the metals are, and cold is better.
posted by OmieWise at 6:15 AM on November 9, 2006

Here in the Netherlands we have had some outbreaks of Legionellosis. Since then showers in public buildings and homes for elderly people are checked regularly.

Some recommendations are: If you do not use the hot water daily, then let the hot water run for a minute to be sure that all 'old' water is gone.
If the hot water is generated via a boiler (containing stagnant water for some time), be sure that the water temperature is above 60 degrees celcius. 'Dead ends' in hot water pipes are dangerous too.

About solved metals in water; Here we hear almost of that kind, only old buildings may have lead pipes. In that case replacement is recommended.
posted by RobHoi at 7:48 AM on November 9, 2006

UK regulations for standard plumbing practices are a bit different from those in the US. Have a look at what our "Drinking Water Inspectorate" says about drinking from storage tanks. If you are in an older house then it is possible that all cold water other than that at the kitchen sink is coming to you via a storage tank. All kinds of things can potentially get into that tank (dust, dead animals, etc).
posted by rongorongo at 8:06 AM on November 9, 2006

-harlequin- writes "(I don't recall the health code safe temperature,"

65C/160F is all that is required to pasturize water.
posted by Mitheral at 8:19 AM on November 9, 2006

Also, using hot water for cooking, with it's higher dissolved mineral content, will deposit more minerals on your pots, accelerating scaling. (more obvious in something like a kettle)
posted by defcom1 at 9:24 AM on November 9, 2006

She maintains that this is because the hot water is usually stored at *warm*, not boiling temperatures, so becoming a much more effective breeding ground for germs than cold water.

Well that's assuming that the water supplied to your house isn't contaminated at the source, the distribution system was set up correctly and the people who take care of the system aren't incompetent buffoon's.
posted by squeak at 10:15 AM on November 9, 2006

65C/160F is all that is required to pasturize water.

and I'm pretty sure most water heaters come stock at 120 F.

(having just had to knock mine up so we could actually fill the bath tub).
posted by fishfucker at 11:29 AM on November 9, 2006

Yeah, and a lot of parenting tips recommend setting your water heater at or lower than 120 to prevent little kids turning up the bath water and scalding themselves.
posted by IndigoRain at 1:35 PM on November 9, 2006

OK, now you guys are confusing me. Is the water cylinder set at the same temperature as the water heater, or is it a separate component designed to stay hotter and thus kill bacteria?
posted by Happydaz at 11:10 PM on November 9, 2006

I'm not sure what a water cylinder is (I believe it's what we would just call a water heater over here), but water heaters are typically stock set at 120F. If 160F is what is required to pasteurize water, well, it ain't doing it.

However, I'm assuming the water coming into your house is already treated in some way, and the point of the water heater is to *heat* water, not to remove bacteria from it. After all, most people drink tap water cold.
posted by fishfucker at 10:47 AM on November 11, 2006

I live in a civilized country where plumbers use hard (silver-based) solder; your mileage may vary.

Less lead is good, but I don't think lead is the only metal to worry about. There will also be other bits of sediment in tanks. A plumber here told me of finding dead rats in home water tanks. Yum! (Rongorongo also alludes to this.)

fishfucker: water is not treated in a way that prevents bacteria from growing in it. The water will be safe when it is flowing straight from the source, but if you leave it stagnating somewhere (say a nice warm tank), bacteria have a chance to grow.
posted by grouse at 9:28 AM on November 12, 2006