decontaminating a heavy metal contaminated stream of water generally the groundwater is used as drinking water in many places without any treatment and is problematic due to its hardness the main source of hardness in water is high concentrations of ca and mg salts it is well known in the art to treat groundwater to remove the dissolved salts in a process often referred to as u201c softening u201d one such process is known as the cold lime soda ash process briefly to soften water by this process lime calcium hydroxide is added to the water to precipitate the calcium bicarbonate as calcium carbonate and the magnesium salts as magnesium hydroxide soda ash sodium carbonate is added to the water to react with the calcium chloride and calcium sulfate originally present in the water as well as that formed by the reaction of lime with magnesium chloride and sulfate the reaction of sodium carbonate with these salts forms calcium carbonate thus the hardness calcium and magnesium salts originally present in the water is partially removed as the slightly soluble compounds calcium carbonate and magnesium hydroxide precipitate out usually a coagulant such as alum sodium aluminate ferric sulfate or suitable polymer is employed in the treatment to assist in the separation of the turbidity precipitates and other solids formed from the water if sterilization and reduction in organic matter are required chlorine is also used in the treatment by suitable modification in the chemical treatment silica reduction can.