Figure a couple gallons a day for each person.
So 2 weeks for 2 people = 14 days x 2 gallons/day x 2 people = 56 gallons.
That's the same calculation that I use, plus some for the dogs.
It used to be that when we lost power, we lost water about 4 hours later because we were on the same power as the water utility company. My solution was to fill a 55 gallon barrel for flushing toilets etc., and to fill several 5 gallon water containers for personal use. Walmart sells 5 gallon collapsible containers that work well in emergencies for very little cash and they don't take up much space in storage. I also have some rigid 5 gallon water containers. If all that fails, I have a bucket filter that's good for about a million gallons and 30,000 gallons of water in the swimming pool. If my lake ever fills up, that's going to have another 25 million gallons in it. I'll be able to get along for a while.
After my bitching at them, my water utility company bought a standby generator to power their pump during a power outage so most of my preparations are redundant ... but I'll keep them anyway. You never know when they'll come in useful again.
Having a backup source of clean drinking water is important. I feel sorry for those people in Toledo right now.
There's also a solution that is added to water that is supposed to keep it pure and drinkable for several months. I think that it's called "water pur" or something like that.