I keep hearing these horror stories about frozen pipes, burst washer
hoses, etc. Scary stuff! So we've decided to shut off the main water
valve in our house whenever we go away for more than a day. We plan to
do this both in summer and in winter.

But I'm not sure what the proper procedure is. Before our last trip, I
turned off the main water valve (the one nearest the water meter) and
then flipped the emergency switch on the water heater (oil fired) so
it wouldn't come on while we were away. I thought we were supposed to
open a faucet to relieve pressure on the system, but when I opened the
kitchen faucet, the water just kept coming out--I expected it to stop
flowing right away, and it didn't, it just kept running. (It was a
single lever faucet--the only kind we have in the house--though I
tried to run only the cold water.) I was afraid we might end up
draining the water heater, so I turned off the faucet again. I don't
know whether it would have stopped running on its own if I'd waited
longer.

So what's the right way to do this? Should we keep a faucet open when
the main valve is turned off? Or will that drain our hot water heater?

Incidentally, I do understand that the *safest* thing in winter would
be to turn off the water, drain the pipes and HWH, put antifreeze in
traps, etc., in case the heat goes out. But realistically speaking,
we're unlikely to do all that every time we go away for a couple of
days, and for longer trips, we arrange for someone to come and check
on the house. All I'm trying to do here is limit the amount of
potential damage in case of a pipe break, etc., while causing minimal
inconvenience.