How much water should I best give to my 6-month-old after feeding solids?

My sister gives an ounce of water a day. Her daughter is feeding solids as well and milk is still her primary nutrition. According to the kid's pedia, an ounce may do so she wouldn't feel so full at all, there can still be room for milk during next feeding time. After all, milk is more nutritious so it's best to be offered more often than water which contains no nutritive value