Which of the following is NOT a method for removing dissolved metals from water?

Activated carbon treatment is primarily designed to remove organic compounds, chlorine, and some specific inorganic substances from water through adsorption. While it may have some efficacy in removing certain metals, it is not a dedicated method for the removal of dissolved metals like some of the other options listed. This method relies on the surface area and chemical properties of the activated carbon and does not target the dissolved metal ions specifically.

On the other hand, cation exchange is a well-established method specifically used to remove positively charged metal ions from water. It involves exchanging these metal ions with sodium or hydrogen ions on a resin. Lime softening also aims to reduce hardness in water caused by dissolved metals like calcium and magnesium by precipitating them as insoluble compounds. Chemical precipitation is another effective method that involves adding chemicals to form insoluble compounds that can be removed from the water.

In this context, activated carbon treatment stands out as the method that is not primarily focused on removing dissolved metals, making it the correct answer.