"Dave, I can't do that" fired this volley in
:

Not sand it is just normal water abrasion. It's why pebbles in streams
are round.

NOSIR! Pebbles in streams are round because they abrade against other
pebbles and sand.

If "normal water erosion" is the culprit, then you either have VERY
alkaline or very acid water. My pump, on a plain string of iron pipe,
lasted 23 years (and probably more) with no such leaks.

Water, all by itself, ain't very abrasive, Dave. Yeah... it can slowly
erode things, but very, very slowly, and certainly not through 3/16" to
1/4" of iron pipe in the time you're quoting.

You have something else going on down there.

Besides... even if 'normal' erosion were the problem, why not seek a
solution to the problem, instead of a way to monitor it?

Lloyd