That's really great that you can go so long between washes, it's a huge first step! And yes, I think what you are currently doing would be considered low 'poo - nothing wrong with that though. If you would like to go no 'poo, I would suggest rye flour or Rhassoul clay hair washes, followed with ACV-water rinses on the ends if you feel it's necessary.
There is plenty of advice out there regarding how to wash your hair with these and I hope these provide a good next step before you go water only. Good luck!