Here in the UK I store water in a cistern in the roof space.
This holds about 200 litres, and is filled with city water automaticly by a float valve as used in a lavatory flush cistern.

An outlet is fitted near the top of the cistern, and this water is used normally for laundry and toilet flushing.
Any interuption in the water supply, would result in the water level in the cistern dropping below the upper outlet, thereby preventing any more water being used for low priority uses.

A second outlet is fitted near the bottom of the cistern, and is connected via microbore copper tube to a water tap in a conclealed place.
The concealement prevents anyone from borrowing, useing, stealing, or requistioning the water.

The reserve capacity is about 150 litres, or enough for drinking for a month or two.
The cistern is kept vlean and has a tight fitting lid, therefore the water should be fit to drink, though I keep chlorine tablets as a second line of defense.