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Subject: TWL: RE: Watermakers and water purity (was Hot water heater story).
From: Robert Bryett (rbryett@XXX.XXX)
Date: Wed May 01 2002 - 22:25:57 EDT
>>>>There is certainly a difference in mechanism and purity between "home"
low pressure Reverse Osmosis Units and a marine high pressure watermaker.
Mel is correct that marine watermakers make water that is very close in
purity to distilled water. The sodium is extremely low--virtually always
less than 500 ppm and in a good functioning water maker less than 200
ppm.<<<<
According to the technical support web sit of a large manufacturer of
reverse osmosis (RO) membrane elements (name and link omitted because I have
an interest in the company), its marine desalination elements "reject" salt
to a minimum of 99.2% when working correctly.
The salinity of seawater varies widely, but I believe the highest "open
water" salinity (i.e. not the Dead Sea) is the Persian Gulf at up to ~40,000
parts per million (ppm). At 99.2% rejection, that would imply that the RO
membrane mentioned above would produce water with a salinity around 350 ppm.
I read somewhere that the WHO recommended a salinity of no more than 1500
ppm for drinking water.
From a corrosion point of view, if you didn't have a watermaker, presumably
you'd fill your water tanks with tap water and feed that to the water
heater. I don't know how different ions affect corrosion, but the
concentration of ions in chlorinated (and in Sydney fluoridized) tap water
is probably higher than in RO water.
Regards, Robert Bryett
Sydney, Australia.
mailto:rbryett@XXX.XXX
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