Now, we are near the water, we have to pump some water.
In order to work, the pump must be immersed. So, first you have to place your pump under the level of water.
Once done, place an atomic compressor next to it, on one of it's side.
Now, use your middle mouse button (or "V" key) to open the inventory of the atomic compressor. You'll see the water getting in the atomic compressor in a slow and steady pace.
Wait some time in order to get a good amount of water. One cube of water can cool down a cube of metal. So, depending on your patience, get some amount of water. The less you'll get, the more you'll have to travel here to get some.
Once you decide you have enough water (or tired to wait), open the atomic compressor inventory and transfert the water cubes in your inventory.
Now, get back to your home, either by using the location system coordinates, or by following the cubes you left on the ground. If you followed advices, your home should be near the 0,0,0 point.
Once you got back home with your water, your mission is over...