That statement might elicit thoughts around nutrition and daily water consumption levels, however this tip is more in line with whether you have the means to provide enough water to you and your loved ones after an interruption. The general recommendation is to have at least 1 gallon of water per person per day. In other words, if you have a household with 4 members, you would need a minimum of 12 gallons (3 days x 4 people = 12 gallons). However, the stress should be placed on that is the minimum. I would encourage you to consider storing for at least 2 weeks.
There are any number of means to establish your emergency water supply and here are a few tips to consider in starting or building upon your inventory.
Low Cost method(s): When I began building our disaster kits, I created a water supply by filling empty pop bottles with tap water. Then I maintained the inventory by emptying and re-filling the bottles every six months. This worked well when I remembered to replenish the supply, but honestly it became time consuming and cumbersome over time.
Potable Water in Your Home Already: If you have the old fashioned water heaters, rather than the newer tankless variety, you have a supply of potable water in your home already. You simply need to learn how to access the water after an interruption. You can also consume the water located in the tanks of your toilets (NOT the bowls).
Convenient method: My husband has jumped on the preparedness band wagon with me, perhaps through no choice of his own, and decided to sign us up for a rotating water supply. We initially ordered six 5-gallon jugs. Of those original six we have rotated with our monthly delivery of a new bottle and so we constantly consume and replenish the water naturally and with little effort on our part to keep it current. You can also purchase bottled water at a grocery store and rotate, as you use them too! We found the jugs to be easier to store and simpler to rotate for expiration purposes.
Filtering Water: If you have access to a body of water, you may want to consider a filtration system! I was recently informed of a system called Berkey and purchased three sport bottle styles for the three members of our household. We live near a fresh water lake and would plan to collect water in bigger containers and then filter when we got back home.
Although this is by no means an all inclusive list of water storage possibilities, it is a starting point and should set you on your way to begin, replenish or enhance your family's emergency water storage inventory!