Only can be one of two things....
pH out of balance, or to dry of air!!! Like a fan blowing on them...
In plants, small pores in leaves - the stomata - take in carbon dioxide for the production of sugars via photosynthesis. These stomata also provide an exit route for the water vapor inside the leaf. A plant with many leaves presents a large surface area capable of losing water vapor. In the desert, a leafy plant would quickly exhaust its water reserves.
Plant leaves don't really take in water. By spraying or by use of a humidifier all your doing really is slowing down the water loss through the leaves.
Try lightly spraying your plants a couple times a day!