You can improvise on almost anything at a retreat except water. Without it, you and your family will become refugees, muy pronto.
If you plan to buy an “in town” retreat, have a long conversation with the City Engineer before making the final selection of a town. Don’t just ask: “Is the water gravity fed?” Nine times out of ten, the engineer will answer yes, but will neglect to mention that it is gravity fed only after it is electrically pumped up hill! You are looking for a town with true end-to-end gravity fed municipal water. Such towns are often found in mountainous regions, or at the base of a mountain range.
If buying an isolated retreat, set your sights on a place with copious spring water or an artesian well. A far less desirable second choice would be a property with well water and/or a true year-round stream. I would rather buy a land with a spring, thin topsoil, and infested with weeds than I would buy place with well water and the best topsoil on earth. Why? Because I can improve topsoil and I can eradicate weeds, but I can’t strike a rock like Moses!
If you are going to have to depend on well water, before you buy the property make sure that the well:
Produces at least 12 gallons per minute (GPM),
Has a stable static level–preferably 40 feet below ground level or less,
Has good water quality (have it tested for both toxins and bacteria!)
Has good southern solar exposure at the well head. (You’ll need this exposure to provide for PV  panels.)
Deep wells are problematic. If you plan to use a deep well with photovoltaic power you are going to need a more complex PV system. Due to the massive voltage line loss inherent with DC cabling, you will either have to add lots of panels or you will have to run an AC pump on an inverter from a DC power source if the well is more than 60 feet deep. Including an inverter in the system adds complexity and is inherently inefficient. Also, keep in mind that if you want a back-up hand pump, you will be limited to a well depth of 40 feet or less.
Two other options for deep wells are a traditional windmill (with sucker rod pump cylinder at the bottom of the shaft, pumping up to a large cistern), or a “jack” type pump. A “jack” pump looks like a miniature oil field “cricket.” Jack pumps use a reciprocating “traveling” arm to actuate a sucker rod connected to a pump cylinder at the bottom of the shaft. (Again, pumping up to a large cistern.) Due to their complex design, jack pumps tend to develop mechanical problems in the long run. Parenthetically, I should add that I had a jack pump for five years, and it was nothing but trouble: fly wheels that flew off, gearboxes that disintegrated, et cetera. I’ll never make that mistake again!