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Comment by Lammy | Hacker News Reader

Anecdote: a plumber in my family swore by this effect and always connected ice makers to the hot water line in new houses. Their justification was that even if their observation was wrong it was still one less thing that was likely to freeze in winter.

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Unless they were inches from the water heater, or had a hot water recirculation system in place:

lol no. Those pipes never even got warm. Ice makers don't use anywhere near enough water to flush even a short line.

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For doing the math! Many ice makers use about four fluid ounces of water per cycle, slightly over 100ml: https://products.geappliances.com/appliance/gea-support-sear...

Per hourly cycle. Or nearly.

When was the last time you turned on the hot water an hour after anyone else used it, and had even the most sightly warmed water within one half to one third of a glass of water?

Never. Even the under-sink heaters hardly work that fast, and their water only has to travel like a meter at most.

The hot water has less dissolved gasses. In some cases it has less chlorine. I put water in a glass pitcher in the fridge because it tastes better after sitting at a lower pressure and off gassing. I agree that the water enters the ice maker at room temperature, but it may not be a bad idea regardless.

If it's heated within a closed system (i.e. mains pressure hot water), the gases are still there - they can only leave the water if you have an open tank, which is a bit old-fashioned. You can observe this by running hot water into a glass from the faucet: it appears cloudy, which is the dissolved gases boiling off.

This means, once the hot water within the pipe has cooled (within the pipe) it'll still have the same gas content as cold water.

Hot water pipes don't have the same potability guarantees as the cold pipes, so this practice would unnecessarily increase your risk of poisoning.

I think that depends where you live. Regulations in my location changed so that hot had to have the same configuration as cold (and supposedly the same potability?). Old houses in the area have separate taps for hot / cold whereas newer houses built after the change have combined hot/cold.

Hot water tanks and heating elements corrode over time.

The tank is lined with glass, it shouldn't corrode unless that surface gets broken.

The sacrificial anode rod is designed to corrode. Depending on its composition that means higher concentration of aluminum or magnesium in the water.

I don’t know why I think this, but I have it in my head that hot water heaters can have more mineral build up. This is why I always thought you should use cold water. Even though the hot was still drinkable, it might be harder water.

I have no idea if this is accurate.

Anecdotally, sometimes your hot water heater or holding tank will rust off a piece and turn your water iron-rich.

Sometimes houses with water softeners will run non-softened water to the cold tap on the kitchen sink for cooking purposes, as some people don't want the salted water.

Yeah hot water can leach metals from the pipes that you really don't want to be drinking. This could either just taste bad, or add unhealthy amounts of lead and copper.

I would not use this plumber.

We are fast approaching a time when all houses have pex. At this point we've been using it in new construction for decades, and most houses with original galvanized pipes are either already replaced with pex, or getting really close.

I'll be honest, I also am not enthusiastic about drinking the volatile organics that hot water leaches out of polyethylene piping.

Give me copper or give me death.

I think you are vastly underestimating the age of the average house.

Correct. Water heaters fill with sediment and should be flushed annually. Of course, nobody does this.

If your water provider says it's potable I'm not going to question it, but I have yet to see a provider that makes such a claim about their hot water. It is difficult to make a statement that would apply worldwide, but where I live, it is easier to keep legionella out of cold water even if the infrastructure for hot and cold is the same.[1]

[1]: [Czech language] https://www.moni.cz/aktuality/tepla-voda-jako-pitna

We are supplied cold water which then goes through a hot water system. My understanding was that the new configuration required the use of check-valves to prevent backflow in such a way as to reduce the risk of cross-contamination between hot/cold. I'm guessing this is now irrelevant because hot water system standards have changed to reduce risk of corrosion / infections occurring, but there is also a chance I was getting mixed up with UK regulations [0].

[0] https://www.bbc.com/news/uk-england-42948046

The hot water tank has a magnesium or aluminum anode. You should ABSOLUTELY not drink that water!!

Find an old tank and open it, and you'll never even consider drinking that water.

In my part of the country, the hot water is softened, so it has an elevated salt content.

Hot water heaters frequently have sacrificial anode rods to prevent corrosion. The rods corrode over time and dissolve into the water. Lower cost aluminum rods have health concerns, not as much with magnesium rods.

See also Tom Scott's video on Britain's history with separate hot and cold taps and why hot taps sometimes had unsanitary cold water tanks to supply them: https://www.youtube.com/watch?v=HfHgUu_8KgA

Depends on your heating system surely?

Recommendations for Belgium: do not drink the hot water

For Geneva: you can drink the hot water

For France: you can drink the hot water but it is disgusting

All of them talk about the same effects (fisdolved oxygen, piping ,...) and come to different conclusions.

My take on that: nobody questions the potability of cold tap water so I will use that one, there is nothing to gain (possibly a shorter time to boil? that trumps the extra cost?)

This thread has revealed an interesting cultural difference, with me being in the minority that gets hot water from a remote provider, as opposed to having a heating system and heating it myself.

wouldn't the refrigerator have to work a lot harder in that case to remove the extra heat? doesn't seem beneficial from an energy use perspective, considering you have to pay to heat the water, then cool it again.

That was my initial reaction too, but upon consideration, how long does it take for hot water to get down the line? Typically, both the hot and cold water lines are full of room-temperature water until you run them long enough to heat up all of the piping between source and sink. I'm having trouble picturing an in-home ice maker having enough throughput for it to actually matter.

This is the reality of the matter, though there may be some minor benefit to "using up" hot water a bit more. Practically it's unlikely to matter either way.

Yes, I’d be pretty pissed off if my plumber did that.

heat isn't real, it's just a measurement of the entropy in a system

if hot water takes shortcuts and freezes faster than cold, then it requires less energy to do so - that is the crux of the debate

> heat isn't real, it's just a measurement of the entropy in a system

You say that as if entropy ain't realy.

> if hot water takes shortcuts and freezes faster than cold, then it requires less energy to do so - that is the crux of the debate

You can't escape the first and second laws of thermodynamics.

It took energy both ways though, first to heat the water and then freeze it. Pretty sure the final bill will not show less energy used.

That sounds like a waste of electricity.

Hot water lines connected to hot water tanks will contain more impurities. Those impurities will slow the melting rate of the ice cubes.

Whaaaattt, whoa. Wouldn't that cause the temperature in the food in the freezer to heat cycle, causing very no bueno bacterial consequences?

No? The freezer is cold without any water connected to the ice maker.

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