Build-up, like scale in kettles gets pretty bad sometimes and that stuff is out the water, right? So I guess I should maybe ask, is it a better or worse idea for health to drink water from a hot water tap or the normal supply? Is a badly scaled coil a reason to bin a kettle?
What is the mineral content of your water supply? Do you have a water softener? If you do is in inline with with the central water line or just the hot water line? Growing up our house had (and still does) naturally hard water. The water softener is only connected to the hot water line. We never experienced any scale with cold water heated in a kettle.
A very small amount of extra stuff can leach out of pipes between the water heater and the tap. Very small. For copper pipes, a truly insignificant amount of copper. The main addition comes from the solder joints which is why lead is banned from plumbing solder now. But still a small amount. Other pipe types and joint material can add their own stuff.
Note that none of these are likely to contribute to scale-type deposits (calcium and such). That comes from the water source. Hot or cold makes no difference.
oddly enough hot water will hold less calcium carbonate than cold water. solubility of calcium carbonate decreases with higher temps. One of the fewish solids to act like this
http://geoinfo.amu.edu.pl/wpk/geos/geo_7/GEO_CHAPTER_7.HTML
http://www.gewater.com/handbook/cooling_water_systems/fig30-4.jsp
I think the above answers are correct in saying that it matters very, very little. If you’re worried about the content of your water, put in a filtration system.
And the main reason you see scale buildup from hot water is that the hot water evaporates much more quickly than cold water, leaving behind mineral solids. I see this all the time in the restaurant business. Steam tables, double boilers, dishwashing machines - all hot applications where the evaporating water is constantly or frequently replaced with more water. Every time you add more water, you’re adding more minerals that then get left behind as the water evaporates, and so it builds up over time.
It’s the same principle as obtaining salt by evaporating seawater.
The reason I was given as a child was that Zinc (from the galvanised hot water cylinder) was present in the heated water.
As a student, I got to test that for my third year inorganic chemistry project - using an electrochemical cell (with a mercury electrode) to measure the zinc content of a variety of different water sources (starting with standardised solutions). As I recall (it was a long time ago) the level of zinc in home hot water wasn’t much higher that that of the cold supply. But zinc levels were high in rainwater supplies that were collected off galvanised iron roofing - the rain was slightly acidic (dissolved CO[sub]2[/sub]) and so leached the zinc, somewhat.
Single data point:
In my CPAP, water that has stood in the hot water tank for a while leaves less deposits than when I use water from the cold side.
Another single data point is that our animals would rather drink long standing water than fresh water from the house. Favorite is rock pools with rain water.
For what it is worth.
This has held true in several different locations.
May have to do with chlorine dissipation??
Back to the OP. Scale (unless it’s really bad) is no reason to toss your kettle. Old family recipe: Boil a cup or so of vinegar with water to fill, let it sit overnight, and boil again. When you pour it out, most of the scale will go with it. Rinse well to get the last of the vinegar.
I don’t have hard water here, but ISTR it working when I was a kid.
This. As it happens, it has become a rather serious problem in my current residence. Fairly hard well water, faucets & fixtures all 50 years old or so, cold water faucets still work fine, hot water faucets produce a bare trickle because of mineral buildup in the faucet valve (the valve forms a severe bottleneck in the line from well to tap and thus is the first place that plugs up). I suspect the faucets will need to be taken apart and de-scaled, or more likely, replaced.
SS
Notably the epa advises to avoid using hot water to reduce lead exposure. The CDC concurrs. This really only applies to older homes which likely still have some lead solder in their pipes. Lead dissolves more readily in warm water, especially warm water that has been sitting there for a while. Better to use the cold tap for health.
Hmm. I should keep that in mind. My apartment building is at least WW2-vintage, possibly older (I have a genuine icebox in the kitchen). OTOH, I mostly drink bottled water, and about the only time I boil water for cooking is when I make pasta.
NO ! The scale on the kettle is where the minerals have settled OUT of the water.
The scale is not going to dissolve back into the water.
Your question didn’t make a lot of sense - if the hot water had more minerals in it, then where did they come from ?
Its advised not to drink the hot water and not to use it for cooking, as some people are particularly intolerant of copper in water, and there is more of the copper (and perhaps lead) in the hot water.
As there is very little copper in our water or food normally, the people who would get sick from DO NOT KNOW they would get sick from it.
This is incorrect, as noted above - scale forms because calcium carbonate is less soluble in hotter water, and isn’t very soluble from solid, which is why it won’t redissolve when the water cools down. Scale is a massive problem in boiler plants and thermal generation facilities, and in many of the problem areas there is no evaporation - the hot water lines are pressurised to allow more heat to be carried without boiling.
I’ve seen recommendations like this before. And there are hosts of similar recommendations from far less august bodies than the CDC and EPA: tea snobs, people selling new hot water heaters, etc.
But I’ve never seen any real data. It must be out there somewhere, right? It should be damn simple data. I.e. in a sample of old houses with lead in the pipes, cold water has X PPB lead, and hot water has X + Y PPB lead. Repeat for other solutes of concern and various types of plumbing systems.
Simple search. http://www.nrcresearchpress.com/doi/abs/10..com
Elevated lead levels all reduced with simple cold water flush in all samples.