RO and entropy

Barry Meyers-Rice (
Mon, 21 Feb 94 15:05:51 MST

Tom in Florida:

Call Culligan (look in the yellow pages) and they'll quote you on a rental.
The advantage there is they'll change your filters yearly, and all that stuff.
Also, Culligan was rated as one of the best units by Consumer Reports. I've
seen the other RO units at our Price Clubs, at about $200, but the Culligan
Unit is about $800 to buy it.

For rentals, they charge me about 25 simolians/month.

Depending upon water quality, RO units discard about 2 liters of water
for every liter they retain as purified. Route this water to your garden
or wherever. It's not toxic, just about 50% enriched in dissolved chemicals.
And while this may seem wasteful, distilled water is pretty damned expensive
w.r.t. energy costs in the distillation process. In terms of ``treading
lightly'' on the Earth, RO is probably more sensible than distilled. Also
call water places (Yellow pages under WATER) to see about buying bottles
of purified water (RO or distilled).

ATT: CHEMISTS---OK, so can someone give me a good explanation of how RO
units use the membrane to purify water? It seems like there's some violations
of entropy going on here!