Tomatoes need to be staked otherwise they will fall over. Yellowed leaves at the bottom of the plant have nothing to do with watering and are not a problem. As the plant grows and its energy goes into making tomatoes, the lower leaves don't get as much food. Tomatoes love water, but the soil must have good drainage. Water in the morning so as not to cause mildew. Soak the soil and when it looks dry, water generously again. in hot weather, you may need to water every other day.