As a watermaker membrane ages and fouls it produces less fresh water but
the salts don't increase. The TDS sensor would divert the product water
if it did get over 200 ppm or so but that is not likely to happen. The
main reason for testing and discarding the first water out is that it
will be salty.

Remember that the process is "REVERSE" osmosis. The high pressure
reverses the natural tendency for salty water to migrate through a
membrane to less salty water. With no pressure the natural process
resumes and salt passes through and accumulates on the fresh water side.

Fred Williams wrote:
Don't really know how your waatermaker works but what happens if the output
goes "sour" after you have sampled and redirected it? I would guess the
"automated" monitor you mentioned is most likely "real time" and should
catch a failure at any time during a watermaker run.

--
Glenn Ashmore

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