In order to move muscle, you need water. Muscle is considered an active tissue and water is found in the highest concentrations in active tissue.
If your body is dehydrated, chances are you're not going to have a very productive weight lifting session. Why? Your muscles are deprived of electrolytes.
Muscles are controlled by nerves.
The electrical stimulation of nerves and contraction of muscles are the result of the exchange of electrolyte minerals dissolved in water.
It's essential that you drink water for building muscle. Without enough water, your muscles are not getting enough electrolytes. Muscle strength and control are weakened. If you want to build muscle, than you must keep your body well hydrated.
Water also helps out with the lubrication of your joints. Water is an ingredient in the makeup of the synovial fluid, which is the lubricating fluid between your joints.
If your weight lifting diet is lacking in water, even for a brief period, less fluid is available to protect these areas.
As you add more weight and stress to your body, the demands from weight lifting on the joints will increase. Adequate protective fluid is essential for optimum performance and to give longer life to your joints. Believe me, once your joints go, its never the same.