The general guideline in earthquake preparedness is to keep a gallon of water per person for three days. That's three gallons per person.
Take stock right now of your family's supply. If you have four people in your family, do you have access to 12 gallons of water in the house? The next time you go to the grocery store, fill a cart with that many gallons just to see what it looks like. Then bring it home.
Unless you have containers specifying the shelf-life of your water, your emergency supply of water should be flushed out every 6 months. It can also be clearly marked and stored and used in an emergency for purposes other than drinking, such as bathing or watering plants after a disaster.
Ask at your workplace about the company supply of water. If there is none, you can start a water drive for employees. Just find a suitable location for storage.
Ask at your children's school about the water supply. If there is none, you can start a water drive for families to provide water. Just find a suitable location for storage.
Keep a water supply in your car at all times. Even if you regularly use it, just get in the habit of regularly replacing it. This is especially true in the summertime.
Remember to keep track of when your water needs replacing and how much you have on hand. Three gallons per person provides a visual you'll get used to noticing.