I have seen water 'Witches' find everything from water, to water lines, to gas lines...
I was a skeptic until in the military I saw a guy 'Witch' out plastic land mines the metal detectors couldn't find!
The guy actually found mines in an area the Engineers/EOD had declared 'Safe', and they were ACTIVE!
Now I'm a believer!
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Old times preferred a Peach Tree limb, but have used about everything from willow to coat hangers to 'Witch' with.
The guy in the military used brass brazing rods instead of copper, said they gave him more 'Sensitivity' what ever that is to a 'Witch'...
Needless to say, we ALWAYS had a supply of brass brazing rods on hand after that!
Water 'Witches' seem to prefer Peach or Willow to find water, and I've not only seen them find water lines, but tell you how deep they are!
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Back to the subject line,
My grandpa used to 'Witch' for well sites, and as far as I know, we never dug a dry hole...
(Dry hole= Well hole that doesn't produce enough water for your needs)
Shallow Wells,
Most old time wells were dug out much larger in diameter than the well walls were going to be,
Then the walls were constructed, and clean gravel was used as fill behind the walls.
That helped even out the pressure on the rock or brick walls, and it helped filter out some of the silt that is going to find it's way into your shallow well.
Rock behind the walls also worked as a 'Reserve' of water that wasn't in the unsupported part of the well, making the actual well much larger in diameter (and larger volume) than the cover or lid let on.
This was often done since the size of a well was often TAXED (and in some European states still is) so the well appeared to be much smaller than it was.
The well was often dug deeper than necessary, and a slab rock bottom put in to work as a 'Stop' when they dipped out the silt from the well.
The rock bottom would tell them when to stop digging, and when the well was 'Dipped' with a hollow tube, it told them how much silt had accumulated in the well.
Shallow wells are particularly susceptible to ground contaminants, so having your well on a hill rather than in a wash or gully would be preferable.
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Deep Wells.
Deep wells are drilled with a derrick, usually a truck mounted version.
It is drilled into hard rock, or an aquifer below the first layers of hard rock.
The top of a deep well is usually a metal tube pressed through the dirt, clay, gravel, ect. to keep that stuff out of the well since it's expensive to have a well drilled, or re-drilled once stuff creeps back into the well over time.
Once the top layers of 'Dirt' are held back with a pipe, then the hard rock drilling can start.
Ideally suited to wells is limestone.
Limestone is ideally suited to filter the water as it migrates through the porous stone, and it's a source of calcium the body can absorb making for strong bones and teeth.
Next I would have to say is Sand Stone.
Good filters, but not as strong and sand stone wells are more likely to collapse in on themselves and/or leak salts or sulfur into the water.
Some people get really lucky, and drill into a rock cave filled with super pure water underground called an 'Aquifer'.
Some of these Aquifers contain super pure water left over from the last ice ages, and in some places they are HUGE!
The rest of us have to be content with 'Ground Water' wells, meaning we have wells that tap into actively cycling ground water, and all the contaminants that brings with it.