On 11/8/2015 2:51 PM, Cal Dershowitz wrote:
I'm turning off supply in a house that is new to me. I think that I'm able to
shut off the supply as it comes into the house. I opened some faucets and let
it drain and flushed a toilet, but it never came to null in terms of flux.

First, it is entirely possible that the "shutoff" doesn't shut, completely.
Many of these (esp older) were gate valves which are notorious for not
shutting off after years of unuse (it's literally a "gate" that slides
down to block the water path through the valve -- calcifications, etc.
end up preventing it from seating completely after longs periods of unuse)

Second, your hot water supply is probably back feeding into the cold
water supply (in the absence of any positive pressure) so there will be some
flow until it, too, is depleted (assuming the shutoff *does* function
properly).

These faucets sit gravitionally-equal to the center of the hot water heater, so
I figure I have to turn off the supply to the hot water heater as well in order
to stop that from wanting to leave the heater.

Look for outdoor hose bibbs as well.

Have I diagnosed my problem correctly, and can I leave the pilot light on for
all this safely? I could have the supply off for as much as a day.

Turn off the water heater if you expect it to drain. You don't want to be
heating an empty vessel!

Resist the temptation to drain the water heater from the "boiler drain"
that is present in the side of the water heater. Again, these things are so
rarely used that you might find *opening* it leaves you with a valve that
you can never *close* properly, afterwards! (why make extra work for
yourself, *now*?)

What's the reason you are turning the water supply off?