For everyone saying that they don't see a point, you've got to look deeper into it.
Basically, the video is showcasing how there are so many different kinds of unconditional love. If you look at the couples dancing together, there's both heterosexual couples and gay couples. Later in the video, you can see a woman with a baby. At one point, there's an elderly woman being taken care of by a younger woman. There's also interracial couples, siblings, and a variety of other different types of people showing unconditional love for one another. Look at the scenes starting at 2:10 on the couches.
The point of the fire and the drowning scenes is that unconditional love can be difficult (see Katy's tweet), but that it's always worth it. There's a lot of symbolism in the video, but it really all does mean something.