The Groundwater Pump is the advanced part of waterworks that permits an expansion of water grid deep into the landmass.
As the name implies, this pump can pull water straight out of ground, no need for adjacent ocean. It`s also producing two and half times more water per tick then Water Pump and has better water storage.
However, all those advantages come with their own shortcomings. To begin with, this pump is eight times more expensive. Other disadvantage is that unlike the Water Pump, Groundwater Pump needs a Water Pipe in order to function - it can not pump water directly into adjacent generators or other pumps. It should be mentioned that the opposite is not true - Water Pump is perfectly able to pump water into the Groundwater Pump.
It should be mentioned that while the pumps share the capacity upgrade with all the other Water Works elements, the upgrades to pump production are separate.