You get this quest in the 2nd gas station, while doing the Seek N Loot main quest.

This sidequest is actually MANDATORY in order to advance the main story line. You CANNOT complete seek'n'loot until you complete Waterdance.

When you arrive at the gas station, you will find the ground covered with electricity sparks. Your goal is to turn off the switches to stop the flow of electricity and clear the way into the gas station.

There are three switches you need to shut down, marked by red flags on the minimap

Switch A:
This is in  a warehouse near the center of the gas station. If you cant find how to get in, go around the fence and jump onto the truck there and over the fence. Enter the shed, there will be some zombies inside including a thug. If you have problem getting rid of them you can just pull them away from the switch, then run to the switch and shut it down. You will need a few seconds to turn off each switch so this approach could take a few tries.

Switch B:
Go to the tunnel on the outer area of gas station. There will be a ladder there - you will have to jump to reach it. Climb up the ladder and turn off the switch

Switch C:
This switch is inside a shed near the main area of the gas station. Turn it off

Once you have turned off all switches, the electric sparks should be clear and you can continue with the Seek N Loot quest.