Harry Bloomfield, Esq. wrote in
:

Fredxx explained :
Rubber washers have a high temperature coefficient of expansion, so
what might be shut off when hot may not be when cold.

The metalwork of the tap will also expand and contract with variations
in temperature. When washing up, I will set the cold tap to dribble to
rinse things. The slow dribble will sometimes stop when the really
cold water gets to the tap.


Tirning the tap more just ends up deforming the washer into the seating.
The washer is just like a lid - pressed "on" should be enough. Tightening
it more only ends up wrecking the washer and wearing the threads.
I used to orient the "H" and "C" into the correct angle when the tap was
turned off sufficietly. I could tell at a glance when my brother in law had
been round as his house wasn't well maintained and he was used to being
brutal with taps.