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?
We are on city water. The timer had previously been installed on another outdoor spigot, and this had never happened.
What to do?