>Although, seeing the inside of an old water heater is all anyone would need to convince them to leave the hot water for washing.

You're talking about all the mineral sediment gunk that accumulates in them? But that's stuff that was in the cold water supply to the water heater but not in the hot water it emitted. It's evidence of its cleaning action.

And you dont want it to clean the seals of pipes, that contain lead. Lead in pipes normally gets a oxide layer that unless disturbed it usually safe, heat disturbs these and causes said problem. Is it realistic to remove every pipe at once? No but they will work on it probably over 10-20 years, since as long as they don't add oxide inhibitors/removers (mostly what caused the flint disaster) or add heat, it is relatively safe.

I think the point is that a cold water line is easily flushed before use, and it's less likely to breed or incubate biologics.

I wouldn't call water standing in accumulated scale and sediment "clean" any more than I'd prefer to drink from a stagnant pool than a stream!

There are places where the hot water is in an open (!) container in the attic and it could have dead rodents, etc. in it. Ireland, for one - which is part of the persistence of separate hot/cold taps in bathrooms.

Hot water is ~never in an open tank. You’re thinking of cold water tanks; historically these were often open, in Ireland and the UK, though this isn’t allowed under modern building regs. However, the water for the hot water tank usually came from the cold water tank, where present, so you have much the same concern. (There are other concerns with hot water tanks, particularly Legionaries Disease, so even if the cold supply is clean the hot may not be.) This is why water from bathroom taps etc isn’t considered drinkable in countries where this is common.

> which is part of the persistence of separate hot/cold taps in bathrooms.

This was a separate but related issue; for a long time plumbing regs required this due to concerns about the possibility of hot water (considered unsafe due to the above) being forced back into the public cold water system. This isn’t possible with modern mixer taps.

I think you might be thinking of the cold water tank in the attic that was historically used to feed decent cold water pressure to the upstairs taps only.

This is why I was told to never drink out of the taps upstairs as a kid. Think these up much rarer these days.

Hot water is always stored in an insulated hotwater cylinder in the UK, not open.

Yes, that's called a header tank. It's common throughout the UK too. It means low water pressure, especially upstairs. The actual hot water is still in an insulated tank within the house. The header tank holds cold water. Most new installations are unvented systems with no header tank, but this comes with its own tradeoffs.

The hot/cold tap thing is funny. We were just taught not to drink from the bathroom tap at all. It still seems gross to me when people do or like in hotels where you have to.

The header tank is to maintain pressurisation in the radiator heating system; modern "combi" boilers don't need a header tank.

Given that many people leave their plumbing/water system in their homes be just the way it is for decades, it's still wise advice.

Anecdotally, many homeowners are unaware of the existence of the sacrificial anode, and suffer premature water heater failure as a result.

Also anecdotally, some water heater replacement specialist contractors take every precaution to keep customers ignorant on this: No post-mortem examination, no mention of the issue, withholding of the printed manual accompanying the new replacement.

To replace the sacrificial anode on my water heater you need to:

1. Dig the plug bolt out from the spray foam insulation with some tiny picks. 2. Get a breaker bar to get enough torque to unseat the nut. 3. Strap the tank to a wall to avoid it moving when using the breaker bar.

The manufacturers don't want you replacing them either. It took over an hour to do something that in theory could take less than 5 minutes.

That said, if you have an non-heat pump electric water heater like mine you're probably better of letting it die and replacing it with a heat pump based model.

Lol, imagining this post-mortem examination cracked me up-- CSI's Bradford White division.

Most homeowners should not be messing with their own plumbing besides fixtures, the commentary on this thread should be more than enough evidence enough for that.

We have a hot water dispenser in one of our kitchen sink popouts; it's tremendously convenient. It's an on-demand heater that makes 82C instantly for tea.