Show how reaction of HCl in water is a reversible reaction?

Use the left-and-right pointing harpoons:

HCl\, \rightleftharpoons \, H^+\, + \, Cl^-

You usually don't show the water unless it's involved in the reaction. Sometimes you put "(aq)" to show it's "aqueous".

HCl(aq)\, \rightleftharpoons \, H^+(aq)\, + \, Cl^-(aq)