I've been in braces for just short of four years (I'm about to get them off). I used a Water Pic sporadically. It is good at removing food, but it be messy and inconvenient to use. I'm not entirely convinced it's a perfect substitute for floss. I would talk to your dentist about it.
I mostly used a combination of Superfloss (way better than floss threaders) and picks and dental brushes of various sizes. I used the Water Pic here and there, mostly when space between my teeth was too tight for floss. I also saw my dentist for a cleaning every four months. The only time I ran into problems is when I had a lot of extra stuff (power chains and the like) that ran right along my gumline. That didn't last long though. An electric toothbrush is also a must.
Congrats on getting braces. I understand all too well what a big step it is. It's been worth it though. Feel free to PM me if you have other questions.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher