Ginny you were close with water running in something, Barbara got it right, she sent me an email with the answer.
The two photos above are on the side of the property and must have been to provide water for the slaves and workers on the plantation and maybe for watering a garden when needed.
Now this is NOT your average cystern, the low building in the above picture is the cystern for the mansion.
Major Gamble didn't trust well water, so he had a massive 40,000 gallon cistern built to accommodate the fresh water needs of the plantation. It included a filtration wall and was stocked with fish to eat the mosquitos and bugs. When slaves would raise the bucket, they had to be sure there were no fish along for the ride.
The cistern still stands and this is the inside view of the cistern, notice it is almost empty, we are still in a drought, during the rainy season it will still hold the 40,000 gallons, MINUS the fish. click on photo to see the dirty water.
Information gathered from Gamble Plantation
We never know the worth of water till the well is dry.
For the Lamb which is in the midst of the throne shall feed them, and shall lead them unto living fountains of waters: and God shall wipe away all tears from their eyes. Revelation 7:17