Great News Jim.... Really pleased for you and the family
He's looking bright!
The amount of fluid you need to take on obviously depends on conditions. I have a 60 mile route where on some days I've drank nothing due to it being too cold, and got through 4 bottles of fluid on other days where it's been really hot. It's worth making a note of places along your training routes where you might be able to refill (e.g. pubs and mini-marts).
If you want to help your body take the fluid on faster you can add third-party electrolytes (e.g. Nuun or Dioralyte) to your bottles or make your own solution (it's harder to make home-made taste anything other than completely rank though). The other advantage of Nuun et al is you can easily carry it around, which is not as easy with a bag of salts.
Glad tosee the little man is doing well ? hope the progress continues.