The Pump

You set out on a week long journey across the desert. You are alone and on foot. On the fourth day, you run out of water. You keep going because you are closer to your destination than to your starting point, but you know that, if you don't find water soon, you will die of thirst.
On the morning of the fifth day, you stumble upon an old wooden shed. Inside, you find an old fashioned mechanical water pump. You try it. Nothing happens.
You look around the shed an find a small bottle of water. It isn't enough to get you across the desert, but you think: "maybe if I'm really careful..."
Then you read the label on the bottle. It says: "Primer. The pump is connected to a well which can give you all the water you need, but it needs to be primed in order to work. There is just enough water in this bottle to prime the pump. Use it wisely.
What do you do and why?