The weather outside's been frightful for many parts of the country this year. Most recently in the northeast, where people found themselves confined to their homes or stranded on the highway in their cars after a whopping blizzard paralyzed parts of Buffalo, New York.

The issue brings to light an important tip: keeping emergency kits handy at home or in your vehicle.

The Federal Emergency Management Agency (FEMA) developed a website dedicated to helping people create and maintain their disaster kits with items such as food, flashlights, first aid supplies, a whistle, dust masks, a manual can opener, and batteries.

You can find their entire recommended list HERE.

But do you know what's critical on that list? Water.

Rather than preparing your own containers of water, the most reliable source is commercially bottled water, stored in a cool, dark place. Mind the expiration dates, of course.

It's recommended to keep a three-day supply of water - per person - available in your emergency kit. Figure about a gallon per day per person, FEMA suggests. That's not a hard and fast rule, however. Here are a few things, per FEMA's guidelines, to keep in mind when planning your emergency water supply: