http://wwwnc.cdc.gov/travel/page/water-disinfection

There are several ways to make water safe, these include heating it, filtering, solar radiation, UV light, and chemicals.

Heating water is a common way to disinfect it, this can be done by boiling it for at least a minute then letting it cool down.

Another way is by putting it through filters. Some filters remove just particles while others remove virus' as well.

Water can also be disinfected by leaving it out in the sun, note that this cannot be done with cloudy water.

Chemicals can be used by placing a tablet in the water which disinfects it, this can be time consuming and take several hours.

UV can be used to kill germs, but is also ineffective in cloudy water.

http://water.epa.gov/learn/kids/drinkingwater/watertreatmentplant_index.cfm

Treatment usually includes Coagulation, Sedimentation, Filtration, Disinfection, and Storage.

Coagulation - Use of putting chemicals in the water to attract dirt, so it can form clumps.

Sedimentation - Clumps of dirt settle at the bottom, so the clear water can continue through the process.

Filtration - Water passes through filters to remove smaller particles.

Disinfection - Chemicals are added to kill left over bacteria.

Storage - The water is piped to communities.