EXTRACTION AND PURIFICATION OF DRINKING WATER

Some consumers choose to purchase bottled drinking water, rather than relying on city tap water

supplies. Bottled water has typically been extracted from underground sources. If water exists underground,

but has no natural exit points, bottling companies may construct a water table well by drilling

down to extract water from an unconfined aquifer. This is done when the Earth’s natural water level

– known as a water table – is much lower than the Earth’s surface. In some cases, as with a valley or

gully on a mountain, the level of the water table may be higher than the Earth’s surface, and a natural

spring can emerge. Bottling companies are permitted to extract this water from a hole drilled into the

underground spring, but the composition of the water must be identical to that of the naturally surfacing

variety nearby.

Artesian water is drawn from a confined aquifer, a deep underground cavity of porous rock that holds

water and bears pressure from a confining layer above it. This water can be accessed if companies drill

a vertical channel down into the confined aquifer. Due to the pressurised nature of this aquifer, water

will often rise up from within it and form a flowing artesian well, which appears as an explosive fountain

at the earth’s surface. However, this only occurs when the surface is lower than the natural water table.

If the surface is not lower than the natural water table, it is still possible to draw artesian water by using

an extraction pump.

Some bottled water is advertised as ‘purified’, which means it has been subjected to a variety of different

cleansing processes. A common filtering procedure, known as reverse osmosis, involves the

water being pressed through microscopic membranes that prevent larger contaminants from passing

through. The microscopic size of these holes is such that they can even obstruct germs, but they are

most effective against undesirable materials such as salt, nitrates and lime scale. One disadvantage

of reverse osmosis is that a lot of unusable water is generated as a by-product of the procedure; this

must be thrown away.

For treating pathogens, an impressive newer option is ultraviolet (UV) light. Powerful UV light has natural

antibacterial qualities, so this process simply requires water to be subjected to a sufficient strength

of UV light as it passes through a treatment chamber. The light neutralises many harmful germs by

removing their DNA, thereby impeding their ability to replicate. A particularly impressive quality of UV

light is its ability to neutralise highly resistant viral agents such as hepatitis.

The overall effects of UV light treatment are variable, however, which leaves many municipal water

treatment processes relying on chlorination. Its powerful and comprehensive antimicrobial effect notwithstanding, chlorination is also extremely inexpensive and remains the only antimicrobial treatment

capable of ensuring water remains contaminant-free all the way through the pipes and to the taps of

domestic homes. Many members of the public remain suspicious of water that has been treated with

such a harsh chemical. Its ease of use and affordability has meant that chlorine often plays an important

role in making tainted water supplies safe for consumption immediately after natural disasters have

occurred.

Some water also undergoes distillation. This involves water being boiled until it converts to steam,

which then passes through a cooling tube and becomes water again. Toxic compounds and impurities

such as heavy metal residue are left behind in this process, so the steamed water is typically cleaner

than the pre-distilled version. Unfortunately, distillation equipment also removes up to fourteen types of

beneficial minerals that naturally occur in water. Consequently, those who rely on distilled water may

need to take mineral supplements.

In developed countries, all forms of drinking water are typically subject to stringent quality control processes,

so there is little evidence to suggest importing bottled water at significant expense will be safer

or healthier than regular tap water from a municipal drinking supply. Both tap water and bottled water

are tested for pathogens and contaminants and, aside from isolated cases related to issues such as

faulty plumbing or old pipes, tap water is harmless. Nevertheless, many purchasers of bottled water still

justify their choice on the quite reasonable basis that tap water has a distinctly unpleasant aftertaste

related to the chlorination process it has undergone.

THE INTERNATIONAL STYLE

A

In the early decades of the 20th century, many Western cities experienced a steep rise in

demand for commercial and civic premises, due to population growth and expansion of the white-collar

professions. At the same time, architects were growing discontented with the ornamental spirals and

decorative features in the prevailing design ethos of art deco or art moderne. Once considered the

height of sophistication, these styles were quickly becoming seen as pretentious and old-fashioned. In

this confluence of movements, a new style of architecture emerged. It was simple, practical and strong;

a new look for the modern city and the modern man. It was named ‘the international style’.

B

Although the international style first emerged in Western Europe in the 1920s, it found its fullest

expression in American architecture and was given its name in a 1932 book of the same title. The first

hints of it in America can be seen on the Empire State Building in New York City, which was completed

in 1931. The top of the building, with its tapered crown, is decidedly art deco, yet the uniform shaft

of the lower two thirds represents a pronounced step in a new direction. Later efforts, such as the

United Nations Secretariat building (1952) and the Seagram Building (1954) came to exemplify the

‘true’ international style.

C

The architects of the international style broke with the past by rejecting virtually all non-essential

ornamentation. They created blockish, flat-roofed skyscrapers using steel, stone and glass. A typical

building facade in this style has an instantly recognisable ribbon design, characterised by strips of floorto-

ceiling windows separated by strips of metal panelling. Interiors showcased open spaces and fluid

movements between separate areas of the building.

D

Fans of the international style of modern buildings celebrated their sleek and economical

contribution to modern cityscapes. While pre-modern architecture was typically designed to display the

wealth and prestige of its landlords or occupants, the international style in some ways exhibited a more

egalitarian tendency. As every building and every floor looked much the same, there was little attempt

to use these designs to make a statement. This focus on function and practicality reflected a desire in

mid-century Western cities to ‘get on with business’ and ‘give everyone a chance’, rather than lauding

the dominant and influential institutions of the day through features such as Romanesque columns.

E

Detractors, however, condemned these buildings for showing little in the way of human spirit or

creativity. For them, the international style represented not an ethos of equality and progress, but an

obsession with profit and ‘the bottom line’ that removed spiritual and creative elements from public life

and public buildings. Under the dominance of the international style, cities became places to work and

do business, but not to express one’s desires or show individuality. It is perhaps telling that while banks

and government departments favoured the international style, arts organisations rarely opted for its

austerity.

rapidly out of favour.

THE MPEMBA EFFECT

In 300 BC, the famous philosopher Aristotle wrote about a strange phenomenon that he had

observed: “Many people, when they want to cool water quickly, begin by putting it in the sun.” Other

philosophers over the ages noted the same result, but were unable to explain it. In 1963, a young

Tanzanian student named Erasto Mpemba noticed that the ice cream he was making froze faster

if the mix was placed in the freezer while warm than if it were at room temperature. He persisted in

questioning why this occurred, and eventually physicist Denis Osborne began a serious investigation

into what is now known as the Mpemba Effect. He and Mpemba co-authored a paper in New Scientist

in 1969, which produced scientific descriptions of some of the many factors at work in freezing water.

It was initially hypothesised that the warm bowl melted itself a place in the ice on the freezer shelf,

thus embedding its base in a ‘nest’ of ice, which would accelerate freezing. The hypothesis was

tested by comparing the result when bowls of warm water were placed on ice and on a dry wire shelf;

this demonstrated that the ice nest actually had little effect. A second suggestion was that the warmer

water would be evaporating at its surface, thus reducing the volume needing to be frozen, but this

idea was also shown to be insignificant. Thermometers placed in the water showed that the cooler

water dropped to freezing temperature well before the warmer bowlful, and yet the latter always froze

solid first. Experiments at different temperatures showed that water at 50C took longest to freeze in a

conventional freezer, while water initially at 350C was quickest.

On further examination, an explanation for this paradox began to emerge. Losing heat from the water

occurs at the points where it is in touch with the colder atmosphere of the freezer, namely the sides of

the bowl and the water surface. A warm surface will lose heat faster than a cold one because of the

contrast between the temperatures; but of course there is more heat to be lost from one bowl than the

other! If the surface can be kept at a higher temperature, the higher rate of heat loss will continue. As

long as the water remains liquid, the cooling portion on top will sink to the bottom of the bowl as the

warmer water below rises to take its place. The early freezing that may occur on the sides and base

of the container will amplify the effect.

The bowl that is more uniformly cold will have far less temperature difference so the water flow

will be minimal. Another inhibiting factor for this container is that ice will also form quite quickly on

the surface. This not only acts as insulation, but will virtually stop the helpful effects of the water

circulating inside the bowl. Ultimately, the rate of cooling the core of this body of water becomes

so slow that the other warmer one is always fully frozen first. While there are limitations to this

comparison (for example, we would not see such a result if one quantity were at 10C and another at

990C) this counter-intuitive result does hold true within the 5–350C range of temperatures indicated

previously.

the question and its underlying explanation continue to fascinate.