Two popular methods of obtaining water are with a well, or with rain water harvesting.
Rain water harvesting depends on appropriate amounts of rain, collector size, storage, and the ability to filter out possible radiological, viral, or particulate (dust, ash, etc.).
A well typically is a more secure method of water, but accessing that water may be an issue in a power down scenario. Deep wells often are the most reliable, and the purest, where shallow wells may dry up in drought conditions, and can be subject to contamination.
We suggest a combination of the two, and a low energy method of obtaining the well water. We also suggest good filtration. We use and recommend the Berkey filter, but a home built slow sand filter could be a lifesaver.
Heated water can be provided with solar, wood fire, or propane, or a combination. A 12v rv pump can be used for pressure, and is cheap to power. It's perfect for pumping from a rain fed cistern. A hand pump as a backup is recommended.