There's a lot that's not formally taught in the US. But I'm in the US and this is a thing. The blended faucets are fine. If it was set to hot or some blend with hot in it, you set it to cold and let it run for 1-3 seconds.

If its not quite hot enough you can end up having a nice incubator for bacteria

Yes, but water coming from the cold water tap has spent less time sitting in that accumulated stuff.

That's why modern kettles can be cleaned. I clean the mineral deposits out of mine once a year or so.

For things like an instapot where you add a cup of water to it, you are actually supposed to use distilled water. I used tap for years with mine and got all sorts of mineralization. It took quite a bit of vinegar to get that off, and now everything looks pristine since I have been using distilled water. You might consider using it for your next kettle, although perhaps the minerals in tap do something to the taste of the tea.

Yes, I didn't say it was lead. It is just a dirty, unpleasant container. Not where you want to get your drinking water, especially for tea.

It isn't just limescale in your hot water heater, it is whatever your water pipe carries in and accumulates in the tank. We lived at the beach and had to flush sand out every couple years.

Unrelated to the tea, but cold water is somewhat safer to drink than water coming from your boiler, that's why.

It's not hot enough. Black tea is usually brewed with boiling hot water around 95 - 100 °C. Green tea is usually brewed a bit lower than that at around 80 °C. But the domestic hot water supply is typically around 50 °C, to prevent burns. It'll be very weak, and probably taste a bit off. Same with coffee, or anything else that requires boiling hot water.

A banana probably has more than enough electrolytes to counter this

Yes, you're right in a pedantic way =). I trust that my city's tap water doesn't have alcohol in it. After all, I previously and many people still drink it without extra filtering, and it's safe enough to do so.

Relatedly, the standard technique in alcohol distillation is to discard the head because it contains toxic methanol. https://youtu.be/a1IruS1bKN8?t=672

>Most modern plumbing heats water on-demand

Where is this the case? These kind of things are extremely locational and here in the US it seems like 45 gallon hot water tanks are still the norm. We had a fad with "on demand" hot water heating but everyone gave up on it when the "it saves you money" part didn't work so well.

I wouldn’t consider on-demand heaters to be all that modern. Places that use on-demand water heaters are now at a disadvantage because it is much more challenging to switch away from fossil fuels over to electric. Tanks, especially with a heat pump, can provide all the heating a household needs through a standard 120V15A socket. For on demand electric water heating you’re looking at upgrading main panels to supply an additional 240V20A and even that will struggle to heat the water enough in some winter climates.

Storage tanks are extremely common in Australia, but they are run hot enough to kill anything and then get mixed with cold water to bring it back to the desired temp.