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Comment by deepsun | Hacker News Reader

Huh? If tap water is contaminated (by, say, metals or salts from plumbing system pipes), then boiling won't decontaminate it either.

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The hot water in your water tank may contain an excess of salt deposits, leeched metals, and rusts that you don't want to consume.

Cold water has less solubility of most substances than hot water and it spends less time sitting in a hot container of those substances.

Therefore, use the cold water to make hot water on your stove and regularly clean the kettle: https://www.reddit.com/r/ThingsCutInHalfPorn/comments/7uu0jz...

> The hot water in your water tank may contain an excess of salt deposits

This is clearly impossible due to conservation of mass, unless you're claiming that the water heater is so hot that it causes nuclear reactions in the water.

Convervation of mass? What do that has to do with it.

Hot water tanks accumilate mineral sediment which might tear of as particles and follow the stream.

? I'm not quite a physicist, but I'm pretty sure this is wrong. The closed system under consideration here consists of both the solute (from the parts of the plumbing system the water has passed through) and the water. If hotter water dissolves more solute, then less solute remains in those parts. What part of this violates conservation of mass?

This is what is in your hot water tank right now.

https://www.youtube.com/watch?v=kAzKts6Wp1Q&t=55s

If your water heater is malfunctioning and not heating up all the way to 140 degrees but it's still heating up to e.g. 100 degrees then it's a breeding ground for listeria. The temperature difference changes the solubility of minerals and salts dissolved in it as well as changing how quickly everything even slightly volatile leaches into the water.

Paradoxically if that is in the tank it means the water coming out must be purer than cold since the contaminats are left in the tank - on average.

In terms of dissolved minerals sure, but there's two important distinctions to make. The tank isn't just accumulating deposits, there's an anode rod inside that's designed as a sacrificial element to protect the tank itself from corrosion. That anode rod gets consumed over the course of a decade so while it's not much, it is being introduced into the water. Also those deposits provide a porous substrate for bacteria to grow on and the heat will help things along.

>> This is what is in your hot water tank right now

Does anyone think the inside of a ~20 year-old cold water feed pipe is going to look shiny and "clean"?

Go take an electron micrograph of the bacteria on your skin, or use a microscope to look closely at the living things inside your bed, in your sofa, or on your pet.

Then take a deep breath, check the causes of death tables if you really have to, and remember that - given we're all intelligent humans - none of these "eww, gross!" things really matter in the overall scheme of things.

Yeah the cold water side will look dramatically better. It certainly will have deposits accumulating but it's not going to be anything close to the amount of deposits that form inside of a water heater. Heating up hard water will chemically alter the water going through it. It's not that those calcium carbonate molecules were in solution before, it's pretty insoluble in water, it's that they were chemically formed when the water was heated.

I'm not suggesting that those deposits are going to kill you or anything, but if things go wrong and the water isn't heated enough those deposits make a great substrate for harmful bacteria to grow.

Ideally you shouldn't use hot water for consumption even though normally it's safe. It also tastes different than cold water because of the change.

I would have had your perspective except that a few months ago I came back from vacation to find that my hot water smelled like windex. The apartment complex flushed my hot water tank, a whole lot of black sludge came out, and my water has been fine since. I assume that not using the hot water for a few weeks caused everything to collect in a concentration high enough to notice, but it makes me cringe to think of how much low level of windex-smelling stuff I drank previously. (Fortunately my hot water takes a minute or two to arrive, so I probably didn’t consume that much just because I didn’t want to wait long enough.)

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