I'm sorry your having trouble with the game. To eat and drink you hold down the right mouse button for a few seconds with the water or food selected in your inventory.
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Hey that's fine. The reason it takes a little while is to make sure people don't accidentality eat the food when they don't mean to, in the early stages of the game food is a little tricky to come by sometimes so while i was developing it i could see people getting frustrated by right clicking to do something and eating there food without wanting to.