We have tomato plants which are like 30 inches or so. The problem is the tomatoes wilt really bad then come back a bit then wilt again. Not sure if they have enough water or too much. Also, does having a water purifier that has salt in it affect the tomato plants as well?
Most likely not enough water. Check the soil. Does it feel damp? Is it soggy? Is is dry and loose to the touch?
Yes, salt in the water can cause problems. The salt can build up in the plant and cause problems and even build up in the soil.
Here are a couple of links for you that will help you.