a flocculant for water treatment containing a highly polymerized silicic acid solution having a high concentration of sio 2 and an extremely low concentration of alkali metal substance , and a method for producing such flocculant . the silicic acid solution is prepared by treating an aqueous solution of an alkali metal silicate such as water glass to remove alkali metal and allowing the solution to liquefy after once gelling . the flocculant may further contain a water soluble metal salt such as ferric chloride or ferric nitrate .