(Saw Adam's reply while posting this, so some duplication of thoughts).
Assuming yours are the typical cases consisting of 24 x .5 liter bottles, you've got between 12-1/2 and 25 gallons of water (converted for us non-metric yanks). Typical recommendations call for between 2 quarts/day per person at the very low end and 1 gallon or more/day per person.
Sufficiency depends on several factors:
• Personal beliefs (we all have an opinion on daily consumption needs).
• Expected duration of the event(s) you're preparing for. Did Katrina influence your thinking?
• Level of exertion during event period (are you helping with, say, tornado clean-up)?
• Climate. Prolonged hot weather expected?
• Individuals in household with special needs.
• Pets in household (they'll need water too).
• Nature of food stored. Moisture-laden foods? Foods requiring water to prepare?
• Supply of non-potable water available for sanitation? Suitable for other personal hygiene needs too?
• Back-up purification methods/equipment included in your preparedness arsenal (and a source of water to purify).
So, under "average" circumstances (whatever that might mean), you have between 6 and 12 days' supply on hand for the two of you. Is that enough? It depends on the severity and duration of the scenarios you're preparing for, and answers to the above points. And how quickly, in the aftermath, you believe services will be restored.
I'd try to keep your on-hand supply closer to the 8 cases rather than 4 cases. At $5/case, that's a modest $20 additional investment. Insurance doesn't come any cheaper than that.
Dan
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"Things that have never happened before happen all the time." — Scott Sagan, The Limits of Safety