This is one of the songs from Sing for Water, someone has just posted it on youtube
It is called Crossing the Bar, it is a poem by Alfred Lord Tennison set to music.
It is only showing the Altos, so unfortunately you can't see me, , I am in the section to the right where we were dressed in sky blue
Whoever took the video must have been stood behind our leader, as you can see her arm conducting from time to time