The common chemical used to purify muddy water to drinking water is 

Key Points

• Potash alum, commonly referred to as aluminum potassium sulphate, is widely used in water purification processes due to its coagulation properties.
• When added to muddy water, potash alum causes suspended particles to coagulate (come together) and settle down, which makes the water clearer.
• This process of coagulation and sedimentation is crucial for the preliminary steps of purifying drinking water, especially in regions lacking advanced water treatment facilities.
• Potash alum not only clarifies water but also has some antibacterial properties, which further contribute to making the water safer for drinking.
• It is preferred in many traditional and rural water purification setups due to its effectiveness, affordability, and ease of use.

Additional Information

• Bleaching powder and chlorine dioxide are also used for water purification, but they primarily function as disinfectants to kill bacteria and other pathogens, rather than clarifying muddy water.
• Copper sulphate is used in some water treatment processes, but its main applications are in algae control in reservoirs and ponds, not in purifying drinking water.
• The choice of chemical for water treatment depends on the specific needs of the water (e.g., clarification, disinfection), the quality of the water being treated, and cost considerations.