I suspect that supplying drinking water to those affected would be well within the capabilities of the civil or military authorities.

A tanker truck holds at least 25,000 litres of water, 100 such trucks each making 10 trips a day can supply 25 million litres a day. In an emergency, such tankers can be hired or requisitioned from dairies, breweries and other industries handling potable liquids in bulk.

Wide bore flexible hose as used by fire fighters can transport a lot of water. A single line of hose with a pump every half mile can transport 10,000 litres an hour, enough for tens of thousands of people.

Providing enough water for firefighting would be more challenging, though the many swimming pools would help.