John
I have shown this to many people, including every plumber I have met.
None of them have ever seen a tap like this.
But to be fair, none of them have ever lived in a house like this.
Never seen this either.
When I was a youngster we had a water softener.
My job was to shovel in salt pellets when needed.
Soft water was a big deal at the time.
We just use city water here.
