[agentwiggles]

> ever start with a hot tap for water you're gonna boil?

I've been told I shouldn't do this, so I don't, but I always feel like a rube waiting for a big pot of pasta water to boil from cold when I know I could have just used my giant tank of heated water and save 10 minutes of waiting...

[sitharus]

That's due to old-fashioned plumbing. Wayyy back in the day when water networks were fairly new they often couldn't provide the water pressure we have now, especially in hilly areas. It was fine for cold water, but not enough to pressurise a hot water tank.

The solution was a header tank in the attic. This stored water from the supply and fed it down to the hot water cylinder, providing some pressure.

The problem is the header tanks weren't a sealed system so animals could make their way in. In particular when using rodent control poison as this makes them seek water. Generally it'd be noticed pretty quickly, but not immediately.

So the hot water was generally safe for washing but shouldn't be used for drinking or cooking.

With modern closed systems (from the 70s onwards really) this isn't an issue.

[coolspot]

Where I am from we are having centrally-heated water, so we were told that hot tap water has anti-scaling chemicals unlike cold tap water which has only excessive chlorine.

[throw0101a]

> With modern closed systems (from the 70s onwards really) this isn't an issue.

The water department for the City of Denver still recommends not to use hot water:

> Hot water systems like tanks and boilers contain metallic parts that corrode as time goes by, contaminating the water. Hot water also dissolves contaminants in pipes faster than cold water.

* https://www.denverwater.org/tap/psa-dont-drink-or-cook-with-...

Also Vancouver (BC):

> Confused, I decided to send the question over to Metro Vancouver, which provides water to most of the 2 million residents in the Vancouver region. Bill Morrell, Metro’s media relations guy, quickly got me this answer from Bob Jones, their water quality expert. The bottom line: Use cold water for boiling.

* https://vancouversun.com/news/staff-blogs/why-you-shouldnt-u...

EPA:

> 2. USE ONLY COLD WATER FOR COOKING AND DRINKING. Do not cook with, or drink water from the hot water tap. Hot water can dissolve more lead more quickly than cold water. If you need hot water, draw water from the cold tap and then heat it.

* https://www.epa.gov/sites/default/files/2015-09/documents/20...

[dabluecaboose]

Worth mentioning that hot water is also better at dissolving things than cold, which is why aquarists should avoid putting anything from the hot water tap into their aquariums. It can introduce copper which is bad for my shrimp.

[myshpa]

I think it's because of the bacteria living in hot water, and some toxins are resistant to boiling.

[yamtaddle]

Yeah, I don't either, but I'd be surprised if most people don't use the hot tap for stovetop-bound water.

[anikom15]

There’s always a chance that there’s a dead animal in your water heater

[gambiting]

I mean.....I don't know about elsewhere, but here in UK you just have a combi boiler, there's no storage.

[anikom15]

Anywhere with abundant natural gas (like America) will mostly have tank water heaters powered by gas.

[yamtaddle]

I'm torn between wanting more information, and preferring to live in blissful ignorance.

[gambiting]

In old houses if you had a hot water storage tank in the attic it was usually just covered with styrofoam or a metal or wooden slab, it wasn't uncommon for an occasional insect or yes, a small rodent to fall in and die in there. It's one of the reasons why most houses in the UK had separate cold and hot water taps - cold water was considered safe to drink, hot not so much.

Nowadays if you have a hot water cylinder it's impossible for anything to get in there(although there is still a chance of bacteria growing inside the tank, but any modern cylinder will periodically heat itself to very high temperature to kill any pathogens)

[dehrmann]

Aren't there occasionally dead animals in NYC rooftop water towers, too? And that's cold water.

[anikom15]

It could be a bird, a bat, or a victim of bipolar disorder.

https://en.m.wikipedia.org/wiki/Death_of_Elisa_Lam

[bmicraft]

No, my water runs through a heat exchanger