@Chef23 I work at the University Hospital in Geneva Switzerland and my wife is a physician as well. Since 5 years, don't ask me why, I work at the library and I have been reading a lot of sudies about back pain an pain related to sport. I am not convinced that an inversion table is going to help you on the long run, maybe just for a few weeks. In the long run, the best you can do for your back is : continue your yoga poses, always good. Then waterski is an unbalanced sport, we have one foot in front of the other, we have a up side down grip, so we need to do some work out to re-balance our body. I believe working hard on the core abdo, the plank and flexion up and down I mean all the way down with your but touching your heels with your arms out. That stretch your back really. Then you can check with your physician if it is muscles related or the spine. Then it is proved tha ointment of comfrey is what is working the best for back pain. I don't know if you have that in the US, let me know I can send you one from here, no problem for me. If you are intersted I can give you more info by my email that you can find on my profile. Hope it will help you.
Chris