I still add a bit of water to my kids food at 9 and 6 mo. The water helps the dry food expand and reduces the chance of bloat (what I was told many yrs ago). It is just a habit and my dogs have eatten dry only when we were out.
When little pups, we added more water than we do now, more because of the new puppy teeth to help them eat and let it sit for a few minutes to soften the food, but quickly moved to just a bit of water, more to just give a bit of gravey but kibble is still hard. But mine seem to prefer the bit of water added, but can go either way.