Christian McArdle wrote:
The stopcock itself has a smallish leak - perhaps enough to lose
half a pint of water per day.

Where is the leak from? What sort of valve is it?

If it is a old style stopcock valve (rather than a lever arm type)
and is leaking from the handle stem, this is quite common and easy to
fix. The stem emerges from a nut on the valve body. Simply tighten
this nut up a bit. It is that simple. If this doesn't stem the leak
(sorry about the pun), then the nut can be removed and new packing
inserted (i.e. lots of PTFE tape). If you don't mind a bit of water,
it is doable even without turning the water off and pretty dry if you
do turn it off.

It's an old-style one. It's similar to the one at
http://www.pettinaroli.com/310nda.htm, but is obviously quite a lot older,
using solder joints.

I will try tightening the nut tomorrow (a touch more water on the floor
can't hurt that much, and the valve is 10 miles away from me) and see how it
goes. The water does appear to be coming from between the nut and the stem.
If needs be, I can then look into getting new packing inserted.

Thanks,
John.