The Grignard reagent is prepared under anhydrous conditions is because of the reaction of the Grignard reagent with water. It reacts very quickly with any proton-containing compound and forms a hydrocarbon. So the effect of the Grignard reagent and its application is lost. The removal of moisture before conducting the preparation is very necessary.

R-Mg-X+H₂O→R-H+Mg(OH)X