Why is it necessary to avoid even traces of moisture from a Grignard reagent? This fact was written in my text book. I wonder why that should be so.
Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons.

$\ce{RMgX + H2O -&gt; RH + Mg(OH)X}$

Where, $\ce{R}$ is a hydrocarbon.