•The running city water in your home, even if the (fuel-driven) pumping continues, may not continue to be properly treated. Whether you get your water from the city, a well, stream, or collect rainwater, you may want to treat the water yourself.
•Earthship ยปFilters can be purchased many places, including a pre-plumbed "Water Organizing Module" available from the "Earthship" people.
•A homemade filter of essentially sand can remove larger particles.
•Water in contact with silver tends to kill microorganisms. Running a small DC current (i.e. from a cheap solar battery charger) through two silver electrodes submerged in the water will distribute silver ions and kill bacteria.
•You can fabricate (or purchase) a still, to use the heat of the sun to evaporate water, then condense the vapor for human consumption. It can be as simple as a sealed bottle setting in the sun, with a hose leading out of it to another bottle, that is buried in shaded soil.
•Expect that you will need to drastically alter your use of water. Washing water can be used to water plants. Eliminate wasting water in the toilet by setting up a composting, or solar dehydrating toilet.