I have gone out a couple of times away from my 7 month DS ... he eats extremely well for a 7 month old (5 solid meals a day - as much as my toddlers) ... anyway, I found he took a bottle of water quite happily until I got home and could feed him (which was 4 hours in one case). I don't do it all the time, but he sometimes has water when he is unsettled and it is enough for him but it is really hot here and all my kids have needed to drink a lot.