Very hard to advise you without seeing a picture of your plant, Basil. But a couple of bits of advice to try:
First, any plant that is in distress should be moved to a shady spot, or at least put one of the bigger plants between it and the window.
Second, the most common problem with newly potted plants is over-watering. The only way to really tell if drainage or too much water is the problem is to carefully slip the plant out of the pot and see if the lower levels of the pot are soggy. IF the soil is wet, you can soak away some of the water with an old towel - just set the plant upright on the folded towel and let it wick the water away (thanks Rick! for this method).
You should definitely not water that baby with well water. Is there any way you can collect some rain water?
A plant that has lived its life in a greenhouse, then is shipped to someone's home where there is most likely air conditioning running will have some trouble adapting to the drier atmosphere. So spraying your new plants with a mist of water occasionally will certainly help them adapt until the weather cools enough so you can let the more moist outside air in.
Further thought, if your night temps are staying warm, you could try putting it outside in bright shade for a week or so, too. But check the above first. If it begins to recover - growth of new leaves is the best indication - you could gradually move it out to a little more sun. Gentle morning sun first.
