J.,
Any child, nursed or formula fed does not need water. They get all the liquids they need from your milk. As well, supplementing with anything between feedings will interfere with your ability to produce milk so it's not a good idea. Solids aren't nutritionally necessary at all, cereal included until at least 6 - 8 months of age. Before that it only detracts from the nutrition your baby gets from your milk and fills up their tummy with empty calories. Just remember you are providing your son with the most nutritionally complete food he will ever need for te first year of his life.
Now, as far as weaning? That is a very personal choice. the AAP states that a year is optimal. Again, this is because nothing can compare nutritionally to the milk only you can provide. Aside from that, of course you can decide for your baby at what point enough is enough. I personally fed my oldest until 14 months, at which point we had an accidental weaning. My second nursed exclusively for 6 months and continued regularly until 2, and still occasionally nurses. My third is 10 months now, was exclusively nursed until 7 1/2 months and still nurses regularly. I personally believe that a child will wean themselves when they are ready. But that's my take on it.
Congratulations on your new one, and kudos for again giving the breastfeeding this a go. I hope your son continues to nurse for as long as you feel is best for him.
Feel free to contact me if you'd like with any questions. And the book that was reccomended is a good one.
Blessings,
Rolinda