Flow pump

Flow pump helps with distributing water from lower ground level to the higher levels. Every pump and Liquid Containers show the level to which they can pump the water, it's called height and you can see in the object info window.

If you build a pump then connect a liquid container to it and build the pipe network from the container, the max height would be counted according to the liquid container. Not according to the pump. So every object you connect to the pipe system resets the height. And that's when you use the flow pump - to improve the max height where you can pump water in the system.