Hot water

[chongalolo]

Is it OK to use hot tap water to fill a kettle?  Please help prevent an argument between me and my son's girlfriend! 

[Hippy]

I do it every time, no ill effects yet. There is a school of thought that says it is not going to be as germ-free as straight from the mains cold, but you are going to boil it, aren't you? I'm sure the hot water tank is only going to hold the bugs that get there in the cold water anyway.

 

[j2buttonsw]

As Hippy says the hot water is often derived from a hot water feeder tank in the loft of your house. If it has been installed to the latest standards it is perfectly OK but, more often than not, they are not: some have no lids, no insullation and no insect resistant air filters. It is not unheard of to find dead pidgeons floating in hot water feeder tanks! Sure, you are boiling the water but getting the water from the kitchen cold tap (which is direct from the cold water mains) is recommended.

[ezapf]

From the Strange-but-True file: cold water boils faster than warm water. Surely someone here can explain the physics behind it. I don't remember how it all goes.

[Headtime]

My mum always advised against this, as we had an old immersion heater that stored the hot water, and was probably full of god knows what inside.

However these days I've got a combi-boiler that draws cold water in from the same mains and heats it instantly, so I suspect that there is no harm in using that to fill a kettle.
I know I certainly do....and no lasting damage has been done to me yet!

[brachiopod]

Depends what you and your son's girlfriend define as 'OK', chongalolo !

 

I wouldn't have a problem using the hot tap to fill a kettle, despite knowing all the possibilities that can occur (pigeons etc) as mentioned, quite correctly, in the posts above. Though I could quite understand why some people might not like the idea !!

The same also applies to tank-fed cold taps. ie those that aren't connected directly to the dry riser (mains). These would be more likely to be found in an upstairs bathroom of an older house (for example, the tap you use to clean your teeth).

[Rabelais]

Warm water certainly does not boil faster than cold. The only physics that cold explain it would be that of an other universe. Under certain specialised conditions hot water can freeze faster than colder water, but only under certain conditions. As for water out of the tank rather than the rising main, it's fresher from the cold tap so why not go for the freshest stuff?

[Pinotage]

It depends; if you have a water heater that heats on demand then OK.

 

But otherwise the water has been kept hot for some time, and is flat and dull. If you take cold water from the kitchen cold tap you are getting fresh water with in it with oxygen trapped in it. Boil that and make tea and you teas with taste better.

 

But why not put it to the test: try both ways and see for yourself ifthere is any taste difference.

[Rabelais]

Oops, that certainly came out all wrong it should have read

"Warm water certainly does boil faster than colder. The only physics that could explain it not doing so would be that of an other universe. Under certain specialised conditions hot water can freeze faster than colder water, but only under certain conditions. As for water out of the tank rather than the rising main, it's fresher from the cold tap so why not go for the freshest stuff?"

I need to adjust my proof reading skills

[natalie_1982]

Why not just use cold water like normal people? 

 

You may have to wait and extra 20-40 seconds for the water to boil, but it is really that important?

[luckystrike]

Exactly natalie_1982.  I totally agree.

[chongalolo]

Thanks everyone for your comments.  I have always only used the cold tap, but she has a 2.1 degree in microbiology.....how could I argue with that? 

[bernardo]

Why not just use cold water like normal people?  
You may have to wait and extra 20-40 seconds for the water to boil, but it is really that important?

 

Think how many cups of tea you have in a lifetime.  Think how many lots of an extra 20 seconds you need to wait.  Think how much time it all adds up to.  Think how many answers you could give in Answerbank in all that time you could have saved.

[natalie_1982]

Perhaps some of us have lives outside of answerbank?

I would have thought a stronger argument would have been how much extra energy I'd be wasting over a life time.

Anyhow, I don't like dead pigeon bits in my tea, even if the bacteria has been boiled out of them.

[ezapf]

Huh, must have been some myth I once heard or I was confusing it with warm water freezing faster under certain conditions.

http://www.madsci.org/posts/archives/mar97/852727758.Ph.r.html

 

[El D]

tea is not supposed to taste as nice if you have used hot water

[mash]

This is all well and good, however not only are there the biology issues but also the environmental ones.

Yes taking hot water saves time, however that water has been heated by another fuel source and then left to cool before you heat again in the kettle.

For the sake of your health and efficiency use mains cold water in your kettle.

[natalie_1982]

Use cold water!  Be normal!

 

• Only fill the kettle with as much as you are going to use
• Do not reboil the same water in a kettle

[kaz35]

As your son's girlfriend has a 2.1 degree in microbiology, surely she could give you a valid reason for NOT putting hot water in the kettle, if there is one? :)

[Kingaroo]

I always thought the reason had nothing to do with sanitation but simply MINERAL DEPOSITS.

Hot water has more minerals dissolved in it (okay this is the part where I'm a little fuzzy, so don't quiz me, I guess it's from the pipes)

As the hot water boils away, the minerals are deposited inside the kettle, causing build up of white crusty scale. Looks nasty, may affect the taste of the water. In an electirc kettle could cause inefficient heat transfer from the coils.

I have heard Japanese monks devoted to the tea ritual would not ever re-boil water because it gets flat or something . They must collect the water fresh and not jostle it as they put it on to boil.

[tell-me-more]

You should ignore your son's girlfriend's qualification, and test what she says as you would any other person. If the qualification is worthwhile, she should be able to explain her reasoning.

Imagine if she'd told you that cold water boils faster than warm water? Would you believe her because of her qualification or would you trust your own experience, which tells you that reboiling a just-boiled kettle takes only a fraction of the time it took to boil in the first place?