design database for restaurant

hey
please see this picture
i design database for restaurant but i think it isn't true
it's only design standard for restaurant system.

i have any problem
1 have different between water and food
water : we buy it and we can check stock
food : we don't buy it and we can't check stock
example :

we buy beer count 10 -> we sale it 5 -> now beer in stock have 5
we buy rice $100,ingredients for food -> we sale it 5-> now instock....

do you understand for i try to say?