So I know you know by now, that I am editing this book because it seems forced and all. I am currently editing book 2 and 4 and soon 3 because I've left out some important factors that I need to put into the books so that the plot could be more impactful. And I have been thinking about changing a few things. So I thought about taking away our lightning bending and let it just be water and blood bending. We are a waterbending master just like Unalaq. Okay, despite your opinion of Unalaq, you can't deny the fact that his waterbending is pure badass.
So, I feel his character is underrated despite of how shitty is. So we have water skills which is exactly like Unalaq's and I think that would be right for the story and I hope you guys like the changes made to the story.
So Bamo is the reason why we can waterbend. So before Vaatu was sealed away, he split himself so that he could find a vessel to destroy Raava. But as the other half spend time in the spirit, it admired the beauty and soon turned good so as a reward, it was gifted the element of water and its purpose is now to serve the Avatar.