Can i use a 5v water pump as a vacuum pump to lift very light objects?
When you say a water pump, do you literally mean a pump designed to move water? If so, then no. Don't bother.

While technically it could have enough suction to do what you want, it is not designed for this application and using a water pump dry will absolutely burn it out (at different lengths of time, from minutes, to hours, to unknown). Depending on the cost of the unit, and the warranty or engineering the manufacturer put in to it (not to mention the parts itself), it could last quite a while. However, most manufacturers have become quite adept at materials manufacturing as their goal is to use as little material as possible, at the least amount of production cost while not producing something "cheap" (to the point people wont rely on it). So a water pump is almost certainly expecting a liquid for cooling. Not to mention the pump mechanism is shaped to move liquid.

This is a scenario where using the proper type of pump for the proper application would in the long run save you money and frustration.