Should I gave my son water during eating or only after?

Start water w/ solid. For the first several months of life, water is unnecessary (and might even be harmful.) a good time to start water is at the same time you start solid, complementary foods like rice cereal between 4-6 months. Offer plain tap water during solid meals, the same way you drink water during your meals. Avoid juice, it's no good for anyone really.
Why give water . Depending on the age of the child & the type of feeding water may or may not be necessary.A breast or bottle fed child that is urinating regularly is getting the nutrition they need without it.A few ounces after feeding may help wash the teeth or the child with firm stools might benefit.I have a few grandmothers that insist on water during the summer & i prefer it to juice as a supplement.