On Sun, 22 Aug 2010 19:29:49 -0700 (PDT), Bryan Scholtes
wrote:

I installed a sprinkler timer on a silcock outside the house, to
irrigate some new grass seed I planted. When the timer turns the water
on, there is a brief episode of water hammer before the water starts
to flow.

Ever since I put the timer on the spigot, there's been black water in
the bathroom fixtures. At first I thought it was a disintegrating
rubber washer in the toilet. But the black water has come out of the
sink and shower too.

The black water goes away after a few seconds.

I imagine I need to flush my hot water heater. But does anyone know
why this might be happening?

It sounds like a coincidence but that still doesn't explain what's
happening. Or maybe the hammer is freeing up dirt somwehere in the
pipes. How old is your house.

We are on city water.

I hear that Blackwater has changed its name to Z, or V. Do you live
in Z or V?

The timer had previously been installed on
another outdoor spigot, and this had never happened.

What to do?

You get water hammer when it turns ON? Not when it turns off? That
doesn't make sense to me. Maybe it's just the water pipe moving
backwards as the water moves forwards, if so it seems to me the
problem would most likely be in the last pipe before the sillcock.
Put your hand on the pipe while someone advances the timer or manually
turns the water on.

Anyhow if it's really water hammer, they sell things that look like
fat brass test tube, 3 or 4 inches long, in the middle of two female
garden faucet connectors, a total of two or three inches long. I have
one on the cold or hot water inlet of my washing machine, because when
I got steel clad hoss to the washing machine, and didn't have mere
rubber anymore, the steel kept the rubber from expanding and absorbing
the shock. Maybe you could put one on the silcock just before the
timer valve, and they also make them to be sweated to copper pipe.