When thinking about self-sufficiency one must consider the basics. This includes shelter, food, and of course water.
The lack of potable (drinkable) water is a concern, especially in developing countries, as the lack of clean water is a major cause of disease and death. The latest stats from UNICEF indicate that 785 million people the world over still lack basic water service and of that number, 144 million still collect drinking water from rivers, lakes and other sources.
There are ways to turn dirty water into usable water. One way, used primarily in the sub-tropics is the use of Moringa seeds (ground into a meal) have the capability to remove suspended solids. The protein in the seeds kills some microbial organisms causing them to clump up in the bottom of the vessel used.
Those of us that don’t live where this is viable ought to know how to make a homemade water filter using common items found on a homestead. You start with a large container such as an old oak barrel (use your imagination as any large vessel will probably do). You then want to mimic nature. How does nature filter water? Think about a watershed. The water flows downhill and large particles such as rocks or tree trunks get stopped by the boulders. Layer one is rocks. Small rocks will do because you will most likely pick out all the larger debris yourself.
Water congregates in pools then slowly seeps into the ground. Layer two is sand. Off-gridders typically take this a step further and use a layer of charcoal. Activated charcoal is the kind most often used for this purpose and NOT the presoaked easy to light stuff in a bag. As an added later you can consider clean pure cotton as a final finish.
The water goes in the top and a spigot at the bottom provides access.
There are variations on this of course. Some use a layer of straw, some forego the rocks.
There’s also distillation over a campfire or solar distillation as well as disinfection through boiling.
There are of course home water distillers (electric) and of course the Berkey line of water filters that use no power and reside on your countertop. If you watch for sales you can often find them bargain priced.
Sure, you can store water whether that’s store bought water by the gallon, those five gallon varieties, home canned water (it’s a thing), your home BOB in the tub, but that won’t last forever. Even a swimming pool full of water will eventually get tainted without a running working filter system. You won’t want to pull your family’s drinking water from a nasty pool.