The 1L includes all fluids, so other liquids (milk) and whatever is in fruits and veges too. DS doesn't drink enough either. I ask him to have a drink every time we leave/enter the rooms where there is a cup, when I have a drink, before we go out, offer his toys a sip too, ask him to 'show his toys how he can drink', ask him whether he wants cold or tap water or water out of Mummy's cup/a grown up cup/water bottle etc