Potable references the cleanliness of water. Potable water is safe for human consumption without any additional filtration or purification methods.
In most developed countries the water that comes into your home has been pre-filtered and treated, making it potable right out of the tap. This includes the water out of your homes hose (as long as your hose is well maintained).
Sometimes the water that gets funneled into your house and local restaurants can be contaminated and declared non-potable.
Bottled water, boxed water, and canned water are all obviously safe choices to use when local waters become undrinkable.