Complex sentence: Commissioners were initially concerned that the water in the area would not be good, the reason from moving the county seat from site on the Sabine River like Pulaski was that they had poor water and were prone to disease and flooding.
Split into simpler sentences: Commissioners were initially concerned that the water in the area would not be good. The reason for moving the county seat from a site on the Sabine River like Pulaski was that it had poor water and was prone to disease and flooding.