I know I have read quite a few directions on boxes for coffee, tea, herbal tea, etc. in my lifetime. And I feel I can safely say all of them say to start with cold water before you boil it. Why is this? Logically, starting with hot tap water would make more sense, if for no other reason than it would boil faster. Why then to all coffee, tea, etc. directions call for boiling cold water?
Thank you in advance to all who reply 
Cold water comes straight from the mains supply through your cold tap.
Therefore it is technically “clean”.
Hot water has gone through your heating system and then put into a tank to sit around for a while. This can pick up sediment/contaminants from the system.
Occasionally my hot water smells funny, musty.
IMHO not something I would recommend you make a cup of tea with.
Additionally, hot water dissolves more contaminants simply because it is hot.
I remember reading during the e. coli scare of the late 90s that you had to cook a burger at a certain temperature for a certain amount of time to kill all the little nasties in it. Maybe if you start with cold water, you can boil off more of the contaminants with the time factor–ie, it takes longer to bring the water to a boil, so the contaminants are exposed to heat longer and thus given more chances to burn up and float off. (WAG)
I think it stems from the use of modern coffee makers. If you start w/ hot water they won’t be as efficient and will produce weaker coffee.
A similar thing I’ve noticed is that the “How to make tea” sites always say to boil fresh water, ie do not reboil water. The reason given is “oxygen content”. I don’t know if this is true.
Years ago I think the county health department recommended not using “hot water” for cooking purposes because more leached lead from soldered copper plumbing and contaminants would be present, though I may be misremembering. At least here, cold water taps in the kitchen are straight from the city service (treated water) and is bacteriologically safe. The hot water tap has gone through the water softener if installed.
This is also what I heard, although I do not remember where.
I had heard that as well, from a Canada Tea Council spokesperson.
Slight Hijack, but if it’s not recommended to use hot water, why do some Hamburger Helper - type foods say to use it?
This is interesting since boiling the water should effectively remove most of the oxygen from the water anyway. Perhaps it only removes some of the oxygen. I reboil water all the time for tea, but I don’t drink much tea.
I’ve no idea whether the “oxygen content” theory is true. However it is certainly true that if you make tea with reboiled, rather than freshly boiled, water, the tea tastes wrong.
Could it have anything to do with a lack of air in the water? I know microwaved water doesn’t always boil because of a lack of nucleation points, so maybe this does something similar if theres no air to start the ball rolling.
If this is the case, then adding your tea/coffee would cause a the water to boil suddenly and violently. You might get hurt, so companies say don’t do it.
Thats my WAG anyway.
Because it cooks faster?
Really? That doesn’t make much sense.
I put hot tapwater in the kettle to make coffee every time, and everybody says they like my coffee.
>Hot water has gone through your heating system and then put into a tank to sit around for a while. This can pick up sediment/contaminants from the system.
Our water’s been sitting underground for thousands of years, I hear, before we bring it up.
If the coffee maker is designed to shut off when the liquid reaches a preset temperature, then starting w/ cold water will mean more circulating time than starting w/ hot water, resulting in a stronger brew.
I’m still not following. Are we talking a drip machine here? I don’t see how it would make a difference. Water gets up to temp, then is dripped into the grounds and the filter. If you start hot or cold, it should still be the same amount of water at the same temperature dripped onto the grounds. The time the water spends in contact with the coffee should be the same, no?
I think the elec. percolator is a better example, although drip makers also carry the cold water reccommendation. Before all these devices were invented, coffee was usually made by placing the coffee into boiling water. When using this method it is common to add a bit of cold water at the end, to settle the grounds to the bottom. Today this is often called hobo coffee.
I think the taboo against using hot tap water, for human consumption, comes from a time when heater tanks were unlined, any contamination caused by modern water heating systems must be very minimal.
I make coffee, tea, and green tea using water from the tap that passes thru a pur water filter. With the green tea there is a substantial difference in taste between filtered/non filtered. Coffee not so much. Hot water from the tap, or water that’s been setting on the stovetop kettle also has a difference in taste (not as good).
Really? You must have pretty nice tap water there, and/or use damn strong coffee.