This paper examines the magnetic and sedimentation properties of a synthetic magnetite developed for water treatment. This was made by the precipitation of a mixture of ferrous and ferric ions with sodium hydroxide at room temperature. The ferrous to ferric ratio was varied between 0.2 and 3.0. Its magnetic properties were compared with iron and other magnetic materials. Experiments show that a permanent magnet placed at the bottom of a settling apparatus greatly speeds up the sedimentation rate in a vessel of 30 cm height. The best range of ferrous to ferric ratio to obtain a high sedimentation velocity is from 1/3 to 2/3.