One of my five tomato plants is wilting in my garden?

The most common problem people tend to have with tomatoes is over-watering. Tomatoes do need a lot of water, but should be watered deeply about once every 10 to 14 days. Daily watering will encourage fungus and wilt. Also, it is not usually a god idea to plant tomatoes in the same place that any solanaceae (tomatoes, potatoes, capsicum, peppers, eggplant) have been grown recently, as the chance of soil-borne pathogens is higher.