Rainwater is far safer than the BPA ridden bottled or municipal water anyway..Get out your clean, preferably BPA free containers and collect gallons. Have your station set up ahead and you will not have any problems if your local grocery is out.
Use your resources around you...they are plentiful..think outside the box...eat the weeds etc..We use half gallon, glass, mason jars on a regular basis and that is all of the drinking water we use in summer. It is amazingly refreshing, zero dissolved solids if collected properly. Use a large plastic sheet if you have a shingle roof ...set something up. So do not panic! Also remember to freeze water ahead to stack in your frig so it will keep things cool once the power goes out!
Then remember to pray like you never have before! This is the month of Elul when you should be thinking of your sins and repenting. Now is as good a time as any!
May God Keep you during this time and always!