When trying to free flow water form one pit to another, it just disappears. On the picture below, there is a wild Contaminated Water pit with 92 tiles (as I recall) with approximatelly 800-900kg of water per tile. Therefore it should easily fill up artificial colony pit.
As you can see, I've attempted to open another area. With the same outcome. When water flowed to the wild pit, it was OK. When it flowed further into artificial pit, then it also disappeared.
I've attached the save file in which first screenshot was made.
See pictures above.