Choice of Words: Water is essential for life. "Need" means to require something in order to exist or function properly. "Alive" means to be living.
Alternative Expressions
Water is necessary for my survival.
Meaning: This means the same as the first sentence. Water is very important for me to live. Without water, I will die.
Choice of Words:Necessary means something that is essential or needed. Survival means the state of continuing to live. When you put them together, "Water is necessary for my survival" means that water is essential for me to continue living.
I cannot live without water.
Meaning: This means the same as the first two sentences. Water is very important for me to live. Without water, I will die.
Choice of Words:Cannot means to be unable to do something. Live means to be alive or have life. When you put them together, "I cannot live without water" means that I am unable to continue living without water.