Purifying drinking water involves removing any contaminants from water sources that may cause harm or that may put levels over the federally mandated levels set for certain chemicals and naturally occurring minerals. The purification methods vary depending on the area and what minerals and chemicals are most prominent in the water source, but usually involve the use of chemicals.
Chloramines and other chlorine like chemicals are the most common way to purify drinking water. Pure chlorine is also a commonly used chemical, but can be toxic if handled in the wrong ways or is present in too high of levels. Both chlorine and chloramines work to kill bacteria and other harmful substances that may be found in drinking water sources.
Chlorine dioxide is another break off from chlorine that can be used to treat and purify drinking water. However, it is not used as often anymore because of both the volatility of the gas that it produces (which is easily combustible), and because it raises the levels of chlorite passed the recommended levels by the United States government.
Hydrogen peroxide is another chemical that is often added to drinking water to help purify it. Hydrogen peroxide is usually combined with an activator called formic acid and works well on harmful protozoans and pathogens in the water supply. However, it takes longer to purify the water than chlorine, and can become a phytotoxin (or a plant poison capable of killing humans in a high enough dosage) if not used properly. It also changes the pH levels of the water, which requires additional chemicals to return the pH back to normal.