In most places in the world the problem is not the lack of water
It is the lack of potable water (drinkable)
Understanding these facts behind water, its availability, and making it potable is the first step to designing a system and methodology that would allow you to survive sustainably off the grid.
Worldwide water consumption has tripled over the past 50 years. According to WHO nearly two-thirds of the world's population will experience water shortage by 2025. 89% of people living in the USA draw their drinking water from public water utilities. The numbers are similar in other industrialized Western Nations. The population explosion in the third world nations such as Africa, India, and the Pacific Rim Nations has caused them to far exceed the capacity of potable ground water. Drawing surface water for drinking water and other basic requirements requires equipment and systems in order to treat the water to make it minimally potable. Uncontrolled population growth unbridled by the constraints of the natural resources necessary to sustain it is rampant and at the heart of the problem.
California is a sterling example. Unsustainable growth, in areas that are unable to support the population has caused it to create shortages in the areas that they draw the water from in the Pacific North West. News reports scream about water poverty and shortages. Such stories miss the point. They create a mindset that they are victims and of course the answer is more regulation and punitive actions. They created their own problem.
Texas had the same problem on the horizon years ago. The difference is that Texas worked in conjunction with businesses and the citizens to act proactively to resolve the problem before it got out of control. The problem for both California and Texas was not a lack of water, but a lack of potable water. Texas years ago began building desalinization plants allowing them to convert the salt water of the Gulf of Mexico into an unlimited source of potable water for their industry and residents. It was a laudable, prudent and proactive approach to assuring their sustainable future.
Human's advancements in ability to treat and purify water have been the foundation of our ability to grow and prosper. The key to learning how to live a self sustained lifestyle is learning how to interact with our environment in a way that leaves the least impact and works in synergy with it as much as possible. The environmentalist movement since the 1970's brought attention to many problems created by the top 1% of businesses and governmental agencies who were destroying the environment with impunity. It also has helped to educate people in how to work more in harmony with the environment. Unfortunately, since the 1990's the environmentalists have been manipulated and used as a weapon of financial warfare picking winners and losers based upon the most current "cause". There is always a need for watchdogs keeping people "straight" but we are all best served by educating and guiding people in ways that benefit them, the economy and the environment. Using less water saves people and businesses money. If someone presents a way to do what is needed without adding cost, labor, and helps the environment few would reject the idea.
Why does that matter? Well, the current approach to environmental protection is through punitive fines and actions instead of partnering with the people to develop better methods. The problem with that is that it draws attention and resources away from understanding the real problem and solutions. Why stop a problem if you are making money off it? Like cigarette taxes and other "sin taxes" if the governments succeeded at making everyone stop smoking there would be a giant hole in the funding resources. It is a conundrum for them.
A classic example is the toilet. It comes in many forms around the world but it is a massive water hog. A family of four can save 45 - 55 gallons of water each day by simply leaving urine in the toilet and only flushing when you need for the rest. That saves 9 - 11 flushes each day. That is why 1992, the United States Congress passed the Energy Policy Act of 1992, which mandated that beginning in 1994 common flush toilets use only 1.6 US gallons (6.1 L). There are many alternatives to the flushing toilet which have been around since the early 1900's. Rather than pushing for the adoption of such technologies governmental agencies have focused on attacking the Western Nations' businesses.
Most groups and governments want you give them power, power to regulate, first "big bad businesses" and then you. It is never enough. They want you to be appalled by the statistic that in order to manufacture blue jeans it requires 2900 gallons of water. Although that sounds horrible it is in fact hype. Having worked for one of the largest garment makers in the world I can tell you first hand that the company's stone wash process reused the water; 75% recovered, then filtered and reused. In addition the company was far more controlled about their water use because it took money off of the bottom-line which they had to explain to their stockholders. That is not to say that businesses do not need to be conscientious and respectful of their impact on the environment and that sometimes they need government regulation to force them if they are not.
Private homes in USA utilize more than half of the potable water delivered by the water utilities; significantly more than business and industry. The government knows that personal homes use far more water frivolously than do businesses.