Instructions
Paint the two boards at the end of the burning building next to Gus to climb onto the rooftop.
Walk across the canal on the rooftop bridge to get on top of the roof of the next building. Spray paint thinner on the discolored section of the wall to reveal the first pump. Spray it with paint to fix it.
Continue walking along the red rooftop, painting missing boards into place where needed. When you reach a rooftop with bars, stand on the bars and spray paint thinner on them to remove them. You will land in a room with the second pump. Spray the second pump with paint to repair it.
Exit the room and jump across the boats to get over the smaller stream. On the far side of the stream, spray paint thinner on the discolored area of the lower wall to reveal the third pump. Fill it with paint to fix it. Once you repair all three pumps, the gate blocking your progress in the canal will unlock and open.