Yeah, Rainbow Dash has mysteriously hurt her wing, but it's happened in the show in "Read it and Weep", so it's easy to think something similar happened here.
This seems like something the two would really do for each other; despite how head-strong Applejack and Rainbow Dash can be, they're still good friends. Splashing around with a water hose would be a great way to cool off during a hot summer's day.
The water effects are really nice without being overdone, and the sun is pronounced but not really obnoxiously so. The ponies look like they're just having so much fun with this.
You know, it's images like this that can always make me smile, no matter what mood I'm in. You did a very good job on this picture, and it makes me glad I didn't just hit "Delete all from MLP:FiM" like I usually do.
The sense of joy that I see in this picture is so uplifting, as well as very very well made, that I just had to tell you in a way that's a lot more detailed than "I love it!" or "It looks amazing!", as well as send a link to my boyfriend, so he could see it too.
The colors used all seem to fit perfectly with one another, and the droplets of free falling water shows a sense of motion and liveliness to the picture. Along with how you made the sun, and it's reflection, makes me Just love to see the picture, as well as add it to my favorites.