Steve is correct, the clay soils in Texas shrink when dry and pull away from the foundations. That leaves no support for the perimeter beams. When the clay gets wet, it expands. To properly water the foundation, you need to start around two or three feet away from the foundation and water slowly, let it expand the clay and push it back up to the foundation. A soaker hose is ideal but automatic sprinklers work well also. People with automatic sprinkler systems have fewer problems than those without them. Pouring water in the crack will do nothing but turn the clay to mush and it won't support anything. The moisture content under the slab is constant and when the perimeter dries out, it allows the edges of the house to sag. When the clay pushes back up to the foundation, you have enough water. If there's a large gap, it may take a couple of days watering. You might also want to check the exposed portion of the foundation and brick veneer for cracks. They will crack before the drywall does.
LJ, we pretty much cleared up BobB's question and think yours is related to the foundation problem. He could also have a leaking water pipe or sewer pipe under the house causing the soil in that area to expand. Just a thought. You'll probably have to remove a tile or two to see what's really happening. Floor wet under the tile, plumbing problem. Floor dry, foundation problem.