It appears at first glance that water is unsuitable for this reaction because aniline is not soluble in water. However, aniline can be made to be soluble in acid after conversion into a water-soluble aminium cation. However nitrogen's nucleophilic unshared electron pair is now bonding to hydrogen so this protonated amino group is no longer reactive as a nucleophile. So sodium acetate is added to the solution of anilinium hydrochloride so produce an equilibrium concentration of aniline below the solubility limit. As free amine reacts with acetic anhydride the equilibrium shifts to the right to make more aniline available for reaction.
Tips Use magnetic stirrers.
If yours has a leak take it to the stockroom and get another. You can share stirrers since the reaction is rapid and they are not in use for the entire reaction. Stirring can be discontinued when you put your flask to warm in 50 C hot water bath. Sodium acetate may be available instead of the trihydrate. When warm return the flask to stirrer when sodium acetate and acetic anhydride are added.