I assume this pipe is vertical and you have access at the surface. I
don't know how accurate this will be, but you could insert a small tube
down the pipe, and once you think you have some water, you could clamp
the tube and pull it out and measure where the water is.
It'd be like putting a straw in a glass of water, putting your finger
over the end, and pulling the water up.
I also wonder if you could use the tube to suck air through it as you
lower it down the pipe. I'd think that when the end hits water, you
might notice a sudden increase in flow resistance, at which point you
could tape or mark the tube and pull out.
The second approach might be more accurate than the first.
And if you don't mind getting some chalk in your water, you can have a
weight pull the end of some string or wire downward. Blue chalk is
rubbed on the line to help easily distinguish wet from dry. The depth
from the surface to the top is calculated by subtracting the length of
the wet part of the tape from the amount of line lowered into the hole.
Take a piece of romex, strip about 1/2" of insulation off the ends of
the black and white wires (and cut back the ground wire if it has one.)
Connect an ohmmeter across the other ends of the black and white wires
and set it to measure maybe 100K ohms full scale.
Lower the romex into the pipe and when the bare ends touch the water
you'll see the resistance indicated by the ohmmeter drop sharply.
You'll be able to move the wire up and down and see the change with a
depth accuracy of maybe an inch.
You could do the same thing with a single conductor wire by measuring
its resistance to ground.
Thanks for the mammaries! Because, about 35 years ago when I was CE for
a company then called "Scully Signal" I designed a "water detector"
based on that principle. I left that job about 25 years ago but I just
Googled "Scully Water Detector", and by gum they're still selling the
damn things. <G>
Get a spool of fishing line, a small fishing weight, and a small
fishing bobber, the long narrow type. I measured one of mine and it
would fit in a 1/2" pipe. If you can't find a small enough bobber, a
6" long piece of 1/4 or 3/8 wood dowel would probably work as well.
Attach the weight to the end of the line, with the bobber a bit
higher. Drop it down until it stops when the bobber hits the water;
mark the line, pull it up and measure from the bobber to the mark.
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