Think before opening a main water fill valve

A pool builder client of ours recently replastered a pool. The job went well and at the end of the day he intended to wash the remaining plaster dust off of the customer's driveway. When he went to use the garden hose, however, he discovered that the main water fill valve was turned off. He opened the ball valve on the fill line and proceeded to wash down the driveway all the time unaware that the plumbing inside the home had been disassembled for an ongoing repair. The driveway was clean . . . the home flooded. Moral to the story: a closed main water fill valve is a red flag. Proceed with caution!