A first essential, daily need to live is pure and drinkable water.
If you have the shameful luxury to flush the toilet several times a day and give fresh water to a lawn it will look like this could not be a problem.
But a whole industry is ensuring the collection, cleaning and distribution of this water.
If this fails you maybe can go on for a little while with bottled water.

waterLater there’s the question whether you can find yourself a well nearby. Or dig a groundwater well. And what degree of contamination it has, or has not. Every year 2.2 million people die from diseases caused by the use of biologically impure water. Besides fairly innocent gastrointestinal disorders, there is also risk of many serious illnesses such as polio, hepatitis A, typhoid fever and cholera.

Maslow's pyramid provides a hierarchical order of needs a man has and pursues. Although subsequent studies give no indication of confirmation I find basic physiological or ’Lower basic needs’an important issue when it comes to survival. Take care of water first, then of food, clothing, warmth, shelter and sleep, then safety and security...
(Pursuing satisfaction of higher needs such as relationships, appreciation, recognition and self-respect are not described here.)

According to some researchers water has an internal memory, the water memory.
In that statement water can store information and even pass it on to other systems / organisms.
Dr. Wolfgang Ludwig: “Drinking water can chemically be clean, but physically considered it can still be charged with information about harmful substances.” Homeopathy also should work with the principle that water passes information.
Rainwater, wastewater and others so will contribute in this vision many years the information from previous situations of its circulation.