How can cholera spread?

Contaminated water. Most people acquire cholera from fecally-contaminated water from an inadequate sewage system or none at all. Haiti, especially after the disastrous earthquake centered in leogane, clearly showed how rapidly cholera can spread without an adequate sewage system.
Fecal-oral. Cholera spreads by the fecal-oral route, meaning infected stool contaminates either food or water consumed by another individual. This is why hand-washing after using the restroom is extremely important! In the US, our water supply is very safe and typically not a cause for concern.