Hi,
Congratulations. I'm not so regimented on fluid intake instead tayloring my intake by the colour of my urine. Keeping the colour between clear to light straw colour signifies your kidneys are getting enough to keep them flushed and doing their job. The darker the urine the more you should drink.
On my best day I managed to push my GFR to 63 but that was on a very strict and restricted diet. Now days I'm more relaxed about the state of my kidneys hovering between stages 3A and 3B. With multiple health issues going on requiring different diets it is not entirely possible to run with a strict diet anymore.
My one big step forward was getting off dark coloured and sugar free sodas, the chemicals used in them are recognised kidney killers. Then no more man made or adulterated foods of the shelf, sticking to fresh and natural where possible.
Cheers