Replenish Ground Water

If Limestone is placed 6 tiles deep over a groundwater source and a Gas Injection Pump is placed over that location then this would help to replenish the groundwater in that location.

Good idea. So that the "Gas injection pump" adds water to the groundwater.

... and it would need a tutorial to explain it to those of us who didn't see it as obvious somehow. :-)

You can use the captain of cheats to replenish the ground and crude deposits.

Groundwater injection pumps use seawater but this would turn the seawater into fresh water. This would completely obsolete desalination.

They could re-name it ground injection pump and have the 2 option. Where the gas only can be on limestone the water could be only allowed to be placed on dirt?

Or add a "fluid pump" that instead to dump fluid in ocean, can pump fluid on ground, so you can make lakes.
If terraforming lakes is too much, the fluid pump could just be used to refill ground water with input clean water, so we can use ground water as water storages.

Add layers of sand, coal, gravel, and limestone, and then sure inject seawater to replenish :)