This could either be a live performance or a video (possibly both).
At Bluestone holiday resort in Wales, they have a swimming pool with a wave machine and large water jets/fountains that spray out in an arc into the pool from a raised platform above the wave-pool.
This performance/filming would happen at night, as lighting is key to its mood.
The pool will start off in low-light-to-darkness.
A soundtrack of Slayer’s ‘Raining Blood’ will play, loud, through the room.
As the track plays, white lights will flash to animate the opening drumbeats of the song.
As the opening riff of the track plays, people dressed in the clothes of heavy metal fans begin to gather on the raised platform (they’re wearing jeans, boots, band t-shirts, cut-off denim jackets with patches).
As the song fully kicks in with Tom Araya’s high pitched scream, the fountains begin spraying into the pool, lit only by red light, and the people amassed on platform begin diving off the platform into the pool, as if stage-diving at a concert.
This continues for 3m25s of the song, until it ends with a huge clap of thunder and the sound of rain.
At this point, the stage-diving stops and the red light changes to white light on the fountains for the remainder of the track (which consists of audio of thunder and rain).