Uses For treating canker sores: powdered alum can be used for treating canker sores. Simply, take a pinch of the powder and apply it to the affected area. It will bring down the pain and heal up the sores quite fast For Purifying Water When a small amount of alum powder is added to water, then the small particles of pollutants present in water tend to stick together and form colloid particles. Since colloid particles are heavy, they easily get settled down at the bottom of the container and the purified water can thus be strained out. Many people living in rural areas use this method to obtain clean water As An Aftershave It is being used as an aftershave for centuries. Take some alum powder and rub it thoroughly all over the freshly shaved face when the skin is still wet. Its astringent qualities will control bleeding from small shaving cuts and thus, prevent infection