Treating brackish water for human consumption “can be done and be done affordably” in New Mexico and other parts of the country, says Mike Hightower, water researcher at Sandia National Laboratories.
“The cost of treating ocean and brackish water has fallen
enough that it can be comparable to the expenses associated with developing new
freshwater supplies,” Hightower says. “It used to cost 50 cents per thousand
gallons of water to supply freshwater. That is now up to $3 to $4 per thousand
of gallons of water – due largely to the fact that fresh water near cities is
generally already being used and utilities frequently have to pump water long
distances, often as far as 100 miles, to get new freshwater supplies. This
raises the cost of new water supplies and the associated price of water.”
At the same time, the cost of treating saline and brackish
water has come down – to $2 to $3 per thousand gallons for water being treated
at the ocean, and $4 to $6 per thousand gallons for inland treatment.
“By the mid ’90s,
you started to see the increasing costs of freshwater intersecting with the
reduced costs of treating saline and brackish water,” Hightower says.
It’s unlikely, however, that future water bills will be
tripling or quadrupling because water that has been desalinized through
processes such as reverse osmosis often will be only used to supplement current
fresh water resources, not as the sole drinking water source for communities.
It will become one of many tools in the toolbox, such as efficiency
improvements and wastewater reuse, to meet future water supply demands.
The use of desalinized water is growing more popular in
places like Alamogordo, N.M., and El Paso, Texas, two communities that sit in
the Tularosa Basin, which contains essentially an underground lake with
brackish water that is 2,000 parts per million to 4,000 parts per million (ppm)
total dissolved solids (TDS), better known as salt. The most easily treatable
form of brackish ground water has from 2,000 ppm to 5,000 ppm TDS, so the
ground water in the Tularosa Basin falls well within the limits.
El Paso recently constructed the world’s largest inland
desalination plant that produces 25 percent of the city’s water, or about 30
million gallons of water a day. Other communities in the Tularosa Basin that
could use this brackish ground water include White Sands Missile Range,
Carrizozo, Corona, Chaparral, N.M., and Horizon City, Texas. Horizon City already
has a working plant, and Alamogordo already has obtained water rights to start
a desalination plant there. Alamogordo also is the location of the Brackish
Groundwater National Desalination Research Facility that opened last year to
support the research and development of new desalination and concentrate
management approaches for brackish ground water.
Brackish ground water identified under Albuquerque’s West
Mesa recently has received a lot of attention, and studies and testing
currently are underway to assess the costs and sustainability of this potential
new water supply. However, the water is more than 10,000 ppm TDS, much higher
than normally considered for cost-effective treatment, and its potential is
being assessed carefully.
Hightower says a 1974 report, “New Mexico Water Resources
Assessment for Planning Purposes,” estimated there are 15 billion acre-feet of
ground water in New Mexico. Seventy-five percent of that is brackish.
“The problem with that estimate is that the brackish water
estimates include water down to 4,000 to 5,000 feet below the surface,” he
says. “Freshwater is generally less than 500 feet below the surface. It is
easier to get the freshwater, and no one has ever really done much pumping of
the brackish waters 4,000 to 5,000 feet deep.
“We may be significantly overestimating the amount of
recoverable brackish water – water that is easy to get to and use,” Hightower
says. “Some analyses suggest that the amount we can recover is only a fraction
of the initial estimate. We won’t know until more testing is done. If it’s not
economically recoverable, the water will not help us much and should not be
According to Hightower, the question frequently asked about
desalination: “Is desalination a silver bullet or pipe dream?”
not a silver bullet and definitely not a pipe dream, either,” he explains. “It
is a reality. In the U.S., desalination treatment has increased by a factor of
four over the past 15 years. Desalination is used in nearly all 50 states and
in many countries all over the world. It is accepted, and can be a
cost-effective approach to supplement current fresh water resources and meet
our future water supply needs. But there are many issues, such as the environmentally
sound disposal of the generated concentrate from desalination, the
sustainability of the supply, and the overall treatment costs, that have to be
carefully evaluated when looking to develop and implement desalination,
especially for inland brackish ground water resources like we have in New
Desalination Could Be Becoming More Affordable
May 14, 2009