At 04:22 PM 2/18/2002, John P. Flaherty wrote:
>Ok, my degree is in business and computers, not science, so I'm certainly
>not an expert, but doesn't water that goes "down the drain" end up back in
>the water supply? If so, in the long term, how is it wasted?

I think it depends on just how "long-term" you're looking at.  Also, taking
municipal water that's already been stored, treated, distributed -- none of
it for free -- and throwing three fourths of it back into the
waste-treatment stream unused is a rather expensive proposition if done in
volume.  It's very easy to make water undrinkable -- not nearly so easy to
make it drinkable again.

There's a lot of water in the world, but comparatively little of it is
fresh, and comparatively little of that is available for use.  Here are
some figures from
http://www.pbs.org/kteh/cadillacdesert/water.html:

>If all the planet's water fit in a gallon jug, available fresh water would
>equal only about a tablespoon. About 93 percent of the planet's water is
>seawater; another 2 percent is locked in ice-caps and glaciers; vast
>reserves of fresh water underlie the planet's surface, but much of it is
>too deep to economically tap.
>
>The earth's total allotment of water has a volume of about 344 million
>cubic miles. Of this:
>
>     * 315 million cubic miles (93%) is sea water!
>     * 9 million cubic miles (2.5%) is in aquifers deep below the earth's
> surface;
>     * 7 million cubic miles (2%) is frozen in polar ice caps;
>     * 53,000 cubic miles of water pass through the planet's lakes and
> streams;
>     * 4,000 cubic miles of water is atmospheric moisture;
>     * 3,400 cubic miles of water are locked within the bodies of living
> things.

And of the available fresh water, the great bulk of it is in Canada and
Russia.  Doesn't leave much for California, which gets a *lot* of water
from out of state.  Do a google on "water wars history" and you'll find
some interesting stuff.

>As population increases, so does the demand for fresh, safe water.
>According to the U.S. Geological Survey, water use in the United States
>alone increased from 330 million gallons a day in 1980 to 408 million
>gallons a day in 1990--a huge leap despite a decade of considerable
>water-rationing.

<snip>

>Agriculture accounts for the bulk of U.S. water use. The average American
>consumes 1,500 pounds of food each year. 1,000 gallons of water are
>required to grow and process each pound of that food. This means that in
>this country, in a single year, an average of 1.5 million gallons of water
>is invested in the food eaten by just one person. This
>200,000-cubic-feet-plus of water-per-person would be enough to cover a
>football field four feet deep.

And irrigation water is a particular difficulty because much of its salt
content remains in the soil, making it gradually saltier and saltier until
it becomes difficult to grow crops on it.

>Industry comes in second with an estimated 28 billion gallons of fresh
>water used everyday--that's seven trillion gallons per year--to make the
>products that are part of our everyday life:
>
>     * 50,000 gallons are required to produce the rayon for an average
> living room carpet;
>     * 40,000 gallons to produce steel for one automobile; 518 gallons for
> one tire;
>     * 1,500 gallons to process a barrel of beer;
>     * 100 gallons to make a pound of cotton;
>     * 55 gallons to make one pound of synthetic rubber;
>     * 24 gallons to make one pound of plastic.

Not a simple problem.  In the case of small reverse-osmosis devices, the
makers judge that customers will be more willing to waste water than to pay
the significant extra costs for units with higher recovery rates.

david

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"