Aurora describe this song as one who came to her in a dream :
"Under the water there is a magical land, filled with wonder. I'm floating on a river and I end up in a place surrounded by a thousand black water lilies. It was a dream I head once. It was originally seven black water lilies... But a thousand sounded better." (^23.1)
"Yeah. “Black Water Lilies” was a dream I had. The melody was playing in the background. And I was dreaming that there was a hand, and I grabbed it, and it took me underwater. And there was a river, under the water, running down. And I floated on the river, under the water, and I came to this magic place with lots of black water lilies – floating on the water – which was underneath the water. It was a very strange dream. When I woke up I ran straight to the piano and wrote the song. So that was a very strange experience, but it only happens a few times." (^23.2)
Berlin music week, September 2014, is the first appearance I have found this song. (^23.3) It wasn't included in her performance at Bylarm in February or at Øya festival in August, so my guess is that this was quite new that year. When released on the album in March 2016, though, it was very well reviewed:
To close the album is the transcendental track “Black Water Lilies.” With a mystical, delicate intro and Aurora’s pure high notes, the entire song is a magical experience. The artist’s vocals flit effortlessly between octaves, creating movement in the music, and even as the arrangement inevitably strengthens to maintain its momentum, it is perpetually fragile, in danger of faltering. Aurora uses water imagery to great effect, with the sobering realisation that the lilies in the water are symbolic of death, however, unlike the more overtly gloomy tracks on the album, this song finds the balance between message and melody necessary to round out the entire collection (^23.4).
Sources
23.1 - Track by track on the 405.
23.2 - Interview with Aurora
23.3 - YouTube - Unknown song / Black water lilies
23.4 - Album review
23 - Aurora Aksnes "Black Water Lilies" at Lowlands, Netherlands 2016.8.21