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Arizona’s Avra Valley is an odd-looking desert. Blooming fields of alfalfa
and cotton spread across its flat landscape even though the annual rainfall
is less than 25 centimetres and tall saguaro cacti fill a national park
just to the south. The valley’s agriculture relies on stores of water deep
underground, but this reservoir is shrinking. To irrigate a hectare of alfalfa,
farmers pump about 15 000 cubic metres of water during each growing season,
enough to flood the land to a depth of 1.5 metres.

To the north and west of Avra Valley, near the towns of Picacho and
Casa Grande, the basins that cradle underground pools of water are smaller.
In half a century of farming, the water table has fallen by 100 metres.
Some wells have run dry, and water from others has turned salty and useless
for irrigation. The rocks that stored the water have contracted and the
land has fallen by as much as 5 metres, fracturing building foundations,roads
and railway beds. Many farmers have abandoned their fields and moved elsewhere.

Farmers have left Avra Valley too, but not because their wells ran dry.
The nearby city of Tucson, with a growing thirst for water, offered ‘top
dollar’ for the land and simply bought them out. In the arid American West,
rights to ground water are tied to land: if you own the land, you can pump
the water. During the past 15 years, Tucson Water, the city’s water supplier,
has purchased 8900 hectares of farmland in the valley. These fields now
lie fallow and deserted. Around them are barbed wire fences and signs to
warn off trespassers and hunters. Tucson Water is not yet using the water
from this area, but the city wanted to stop the farmers from pumping it
out.

Every sale makes life harder for those who remain. When farmers pull
out, the local economy gradually dries up as businesses and stores abandon
the area. But that does not bother Kirke Guild, a manager at Tucson Water.
He says the farms that the city has taken out of production were using 154
million cubic metres of water a year – more than the entire commercial and
residential consumption of Tucson in the 1970s, when the city started buying
farms.

Water has always been at the centre of local politics in arid regions
of the American southwest. As one Californian farmer put it: ‘Around here,
whisky’s for drinking, and water’s for fighting.’ Once, the federal government
built dams and canals that provided water to farmers at cut-price rates.
But in recent years, the limits on water supply have become clear. The era
of cheap and abundant water is ending.

Most rivers have already been dammed and laws now limit the use of ground
water. Desert cities such as Tucson, Phoenix and Los Angeles are using their
financial power to wrest control of water away from farmers. Even so, they
are beginning to worry that their water may not last through the next century.
Unless their citizens learn to live with a fraction of the water they currently
consume, the cities could turn into ghost towns – boarded up like those
old settlements around Picacho and Casa Grande.

Tucson, with a population of 600 000, is the largest city in the US
that relies on ground water for its entire water supply. It pumps 370 million
cubic metres of water out of the ground each year; 130 million cubic metres
serve the needs of its citizens and the rest is for the region’s agriculture
and industry. The US Geological Survey estimates that natural sources, such
as rain and melting snow from nearby mountain ranges, replace less than
half this water. The water table under Tucson has been falling by an average
of 1 metre a year since large-scale exploitation of the city’s aquifers
began half a century ago. But Guild says there is no immediate crisis. ‘This
is the most-studied ground water basin in the US,’ he notes, and the remaining
reserves of water are immense. The water table now lies about 70 metres
below the surface, but the city’s wells reach a depth of 250 metres, and
the reservoir of water is much deeper than that. The first 400 metres below
the top of the water table contain 111 billion cubic metres of water, says
Guild. This is 15 times the amount of water that Tucson has mined from its
underground reservoirs over 50 years. And that is not the bottom of the
reservoir; it extends down to depths of 700 metres or more, adds Guild.

But there is no room for complacency. Saline water, because it is more
dense, collects at the bottom of geological basins. The deeper the city
drills, the worse the water quality. The costs of operating wells increase
as the water table sinks because it takes an enormous amount of energy to
lift columns of water long distances to the surface. Tucson currently spends
$40 to pump 1000 cubic metres of water – enough for about two average families
of three in the city for one year – and that cost would double if the depth
of the water table doubled. Tightly packed soil at lower depths also blocks
the free flow of water, so wells cannot draw water as efficiently from the
surrounding earth. ‘Tucson is probably okay for another 50 years, maybe
100 years,’ says Stan Davis, a hydrologist at the University of Arizona
in the city. But in the life of ground water deposits, a century is a short
time. Some of the water under Tucson has been there for several thousand
years.

To stop profligate waste of water reserves, Arizona passed an ambitious
law in 1980 called the Groundwater Management Act. Under the law, the state’s
Department of Water Resources installed a meter on every well and set limits
on the amount of ground water that each city, farm or company can draw from
the wells it owns. Cities and farms in Arizona are supposed to achieve ‘safe
yields’ of ground water by 2025. This means no more water would be taken
out of aquifers than is naturally replenished. Kath-ryn Jacobs, director
of the Tucson office of the Department of Water Resources, admits that this
is a ‘tall order’. The cities of Tucson and Phoenix are far from that goal
now, and their populations, according to official estimates, will triple
by 2025.

Tucson, in fact, currently violates the law. In the early 1970s, a campaign
to promote conservation of water in the city cut consumption from 680 litres
per person per day to 606 litres. State regulators set a target of 587 litres
by 1987, but a series of hot, dry summers pushed up consumption to 625 litres.
Under the law, Tucson could be fined $10 000 each day, but the state has
waived the fine. Tucson, however, is doing better than Phoenix, where the
average resident consumes 984 litres a day, or Las Vegas, whose thirsty
citizens soak up 1287 litres.

Phoenix, far more than Tucson, seems intent on denying the fact that
it is built in a desert. People often move there for the clear air, dry
climate and mild winters; but they do not want to give up lush golf courses,
tall trees and swimming pools. Corporate headquarters and housing developments
in Phoenix are frequently built around water fountains and large lawns.
Each square metre of grassy lawn requires about 11 litres of water each
year.

Early in 1991, Tucson adopted new laws that forbid such extravagances
in new construction. No more than 10 per cent of the landscape around new
developments can be planted with grass and only then if the grass fulfils
some function, such as a place to sit and eat lunch. New houses are required
to use more efficient toilets, taps and showers. The city will contribute
to the cost of a family toilet that uses only 6 litres when flushed. Older
American toilets use nearly four times as much.

Tucson recycled 6.4 million cubic metres of waste water last year for
watering golf courses and for industrial cooling. The amount of recycled
effluent will increase fivefold in 15 years, says Guild. Much of it will
go to replenish the aquifer. After initial treatment, the water will be
poured into huge basins dug on the surface. As it soaks through the earth,
bacteria degrade many chemicals, and other pollutants are trapped in the
pores of the soil or bind to particles, so that the water is filtered and
purified by the time it reaches the aquifer. Eventually, more effective
chemical treatment of effluent could allow Tucson to use recycled water
directly as drinking water.

To encourage people in Tucson to save more water, Tucson Water and a
citizen’s group called the Southwest Arizona Water Resources Association
(SAWARA) set up a demonstration house in 1985. ‘We show people the easy
ways to save water,’ says Glenn France, who lives in Casa del Agua (House
of Water) with his wife and their child. Water conservation at the house
results almost entirely from technology, not from changes in lifestyle.
The family uses only half as much water from the city’s wells as a typical
family of three in Tucson. Water collected from the roof and a recycling
system that reclaims water from washing dishes and baths is used to water
plants and a small lawn.

SAWARA promotes a land-scaping philosophy it calls Xeriscape, derived
from the Greek word xeros, meaning dry. Instead of using green grass and
willow trees, landscapers in arid regions should rely on the charms of colourful
rocks, tiles and plants that do not need much water, says Marybeth Carlile,
executive director of SAWARA. The association has put together a list of
such plants, ranging from mesquite trees to desert honeysuckle and prickly
pear.

Harsher conservation steps that could threaten the local economy, however,
touch a sensitive nerve. In 1976, Tucson’s city council doubled water bills
and, in the political uproar that followed, the entire council was voted
out of office.

Water in Tucson now costs at least 50 per cent more than it does in
Phoenix, though it is no more expensive than water in cities on the east
coast of the US, such as Boston, where it is far more abundant but requires
more treatment. Gary Woodard, an economist at the University of Arizona,
has found that increasing the price of water by 10 per cent causes consumers
to use 6 per cent less.

Now an apparent solution to Tucson’s water troubles is on the horizon.
The Central Arizona Project, an enormous canal that diverts water from the
Colorado River, 350 kilometres away, recently reached Tucson. As soon as
a treatment plant for the water is finished in about a year’s time, the
city plans to use an annual allotment of 183 million cubic metres and, for
now, pour two-thirds of it into aquifers for long-term storage.

But water from the canal, even after it is treated, will be of lower
quality than Tucson’s ground water. It will contain far higher levels of
sulphates and salt and, although some of this will be filtered out as it
percolates through the soil, it will eventually lower water quality in the
aquifer. However, the positive aspect of this project is that, at one stroke,
it will remove Tucson’s dependence on ground water and bring the city into
compliance with Arizona’s Groundwater Management Act. ‘The Central Arizona
Project is this great panacea,’ says Tom Maddock, a professor of hydrology
at the University of Arizona in Tucson. It could satisfy Tucson’s thirst
for decades. But unless the city finds ways to conserve and recycle more
water, it will have to start draining its underground reservoir again within
50 years.

The people most unhappy about the canal are in California. Until now,
Los Angeles and the large agricultural irrigation districts of southern
California used part of Arizona’s allotment of Colorado water, along with
their own. Now, just as California is in the middle of its worst water shortage
in decades, Arizona is planning to take up its full quota of the river’s
water for the first time.

In the past, government policies were based on the idea that access
to water from streams and underground aquifers was a basic right. Government
agencies often sold water to farmers for much less than the cost of building
the dams and canals that helped to provide it. Increasingly, however, scarce
water is becoming a commodity that is sold to the highest bidder, and its
price will dictate how it is used. ‘People need to know that water is going
to get more expensive, forever,’ says Carlile. Farmers have become accustomed
to pumping ground water cheaply; it can cost them as little as $28 per
1000 cubic metres when the water does not lie far below the surface. But
under controls established by the law, their rights to use this water will
be increasingly restricted.

Sales of water from the Central Arizona Project are supposed to cover
its construction cost. Farmers will pay $62 per 1000 cubic metres for the
water, and industrial customers twice that. Other water sources, however,
are even more expensive. Treated waste water that is suitable for irrigation,
but not for drinking, costs $213. If it is treated well enough to serve
as drinking water, the cost doubles.

Farmers will be the first casualties of high water prices, and some
kinds of heavy industry, such as a complex of copper smelters south of Tucson,
may not be far behind. Households may protest about the high prices, but
water will still be a minor part of their total spending. Higher prices
will, however, make it worthwhile installing technology to conserve water,
such as storage tanks that collect rainwater during the storms that sweep
through the desert every July and August.

In California, Santa Barbara plans to tap the most expensive water source
of all: the ocean. It has ordered a desalination plant that, from next year,
will be turning 12 million cubic metres of ocean brine each year into drinking
water. The plant will be the first large-scale effort in the US to extract
drinkable water from the ocean. Ionics, the company building the $36 million
plant, will sell its water to Santa Barbara for $2344 per 1000 cubic metres.
At that price, irrigating a hectare of alfalfa for a year, which will sell
for only about $1100, would cost more than $35 000. Water for a load of
laundry would cost about 50 cents, instead of less than 2 cents.

California’s drought, now in its fifth year, made Santa Barbara desperate
for new sources of water for its population of 85 000. ‘We needed something
as quickly as possible,’ says Lisa Weeks, an official with the city’s Department
of Public Works. The situation became less dire in March, when California
got more rain than it had seen in any month since 1986. By February the
city’s reservoir had been dry for months, and Lake Cachuma, an artificial
lake built in 1951 from which the city draws most of its water, was down
to 14 per cent of its capacity. But even after the ‘March miracle’, Lake
Cachuma was back to only about half its normal level, and the rains have
ended for another year. Santa Barbara still plans to go ahead with the plant
in case the rains of last March mark only a brief respite in the drought.

In the American southwest, people have not yet been forced to take such
extreme steps. But sooner or later, depending on how efficiently they use
the water they have, the settlements in these arid areas will have to come
to terms with the limits that nature sets, using only the water that falls
from the sky each year.

* * *

Ground water pollution . . . contamination that never clears

Tucson, more than most cities, must protect its underground reservoirs
from contamination with toxic chemicals. Ground water is its lifeblood.
So when high concentrations of the solvent tri-chloroethylene (TCE) turned
up in an aquifer under Tucson in 1981, the city was stunned. The solvent,
which the Environmental Protection Agency considers a possible human carcinogen,
had been dumped or had leaked from aerospace companies and from an air force
base nearby.

By the time the pollution was discovered, contaminated water had spread
in a plume, 6.5 kilometres long and 1 kilometre wide, under the west side
of the city. Fortunately, the TCE was contained in a shallow aquifer, separated
by clay from a deep aquifer that holds much more water. Near the source
of the contamination, concentrations of TCE reached 15 000 parts per billion.
The EPA’s drinking water standard for TCE is 1.5 parts per billon.

Tucson Water shut down nine wells threatened by the plume, representing
about 3 per cent of its water supply. The city then drilled a set of wells
to pump out contaminated water and treat it. The plume’s growth was halted
by 1986 and concentrations of TCE in the water are gradually being reduced.
The city plans to keep pumping water out of the aquifer and treating it
for another 20 years.

Similar stories haunt almost every large city in the US, and many small
towns as well. For once aquifers are polluted, they are always polluted.
A survey in 1989 of 19 sites where the EPA has tried to remove pollution
from ground water found that pumping away the contaminated water for treatment
brings the concentration of pollutants down by 50 to 90 per cent, but no
more.

When the contaminated water has been brought to the surface, the simplest
kind of treatment for volatile chemicals, such as TCE, is to let them evaporate
into the air. In Tucson, the contaminated air is pumped through a filter
that collects the TCE. In some places, contaminated water is exposed to
intense ultraviolet light or heat. ¿ìè¶ÌÊÓƵs at Sandia National Laboratories
in New Mexico have built an array of mirrors that reflect sunlight towards
transparent tubes where contaminated water circulates. Concentrated heat
from the sun breaks down many toxic compounds into carbon dioxide, chlorine
and water.

‘If you can get it to the surface, you can deal with it. You have plenty
of options,’ says Dick Scalf, who manages research on ground water pollution
at the EPA’s laboratory in Ada, Oklahoma. ‘The problem is getting it to
the surface.’

Scalf compares extracting contaminated water to drilling for oil. Even
the best oil extraction techniques leave 30 per cent of the oil in the ground.
Similarly, pollution may remain in oily clumps that are not dissolved in
the water. Contaminants may attach themselves to particles of soil, or they
may become trapped in pockets of water that are separated from the rest
of the aquifer.

Much of the EPA’s research is devoted to developing ways of removing
pollution from aquifers without drawing the contaminated water to the surface
first. Many of these approaches involve existing or genetically engineered
bacteria. In some cases, nutrients are injected into the aquifer to encourage
the microbes to grow. Some forms of pollution, such as that created by oil
spills, are more easily attacked in this way because naturally occurring
bacteria can degrade them. For other toxic compounds, no such microbes exist.

But while hundreds of millions of dollars are spent each year cleaning
up contaminated aquifers, some scientists think that much of it could be
better spent. In 9 out of 10 sites where the EPA is treating polluted ground
water, there is no projected risk to human health. And in most of these,
the risk was unchanged after millions of dollars were spent.

The EPA released a statement of priorities late last year that called
ground water pollution a ‘low-risk problem’. The levels of contamination
are often low, the toxicity of the chemicals is in dispute, and the contamination
is often in isolated areas where there are no wells.

In many agricultural areas, the most serious threats to ground water
do not come from industrial waste, but from the gradual leaching of salt
and nitrates from fields into the aquifer. These sources of pollution are
also hard to control because they do not come from a single source. Irrigated
agriculture causes salt to build up in soil because most of the water evaporates
away, leaving behind the salts that were dissolved in the water.