Random water leak in kitchen

[Virginia Jones]

I'm in the process of renovating my first rental house Right now the kitchen is torn down to the studs. The sink valves have been turned off and not touched for days. Every time I work on the house I usually turn the water to the whole house on when I arrive and turn it off when I leave.

Today, an hour after I turned it on, I heard water dripping. I went into the kitchen and there was water spraying up from the sink pipe. (no sink attached to it and valve was turned off)

Does anyone know how this happened and why it randomly happened over an hour after the water being on??

The water supply to the kitchen is right above the breaker box in the basement and there was water pouring down over all of the electrical wires and behind the box.