Re: Why do plants need water?

Plants use water in several different ways, including:
1. Water is a solvent for biochemical reactions.
2. Water is required or produced by many biochemical reactions.
3. Water flow helps transport mineral nutrients through the plant.
4. Water filled cells help support the plant, therefore plants deprived of water 
wilt.
5. About 95% of water absorbed by most plants is evaporated from the leaves 
(termed transpiration) because the stomata must be open to let in carbon dioxide 
needed for photosynthesis.

Liquid fertilizer has mineral nutrient salts in it, and salts lower the water 
potential. Water moves from high water potential to lower (usually more 
negative) water potential. Therefore, you may expect that wilted plants will 
recover better when receiving plain water. However, plants also require mineral 
nutrients that fertilizer contains. If the liquid fertilizer is concentrated 
enough, it will certainly reduce the rate of recovery or prevent recovery. You 
also have to be sure all your plants are wilted to the same extent, which is not 
that easy to do.

Reference

Stern, K.R. 1991. Introductory Plant Biology. Dubuque, IA: Wm. C. Brown.