IELTS Academic Reading Practice Test 402

Before piped water and sewers became normal in European cities, typhoid fever was among the most feared of infectious diseases. It is caused by a bacterium, Salmonella Typhi, which is passed in the faeces of infected people and reaches new victims through water or food that has been contaminated. The illness begins with headache and loss of appetite, and the fever climbs steadily during the first week. In the era before antibiotics perhaps one patient in five died, and some of those who recovered continued to carry the bacteria, shedding them for years afterwards.

The physician who did most to produce a defence against the disease was Almroth Wright. Born in 1861 in the village of Middleton Tyas in Yorkshire, the son of a clergyman, he studied medicine in Dublin and then spent time in Germany, where the laboratories of the great bacteriologists were transforming the subject. In 1892 he was appointed professor of pathology at the Army Medical School at Netley, on the south coast of England, and it was there that he began to think seriously about the infections that killed soldiers in wartime.

Armies had particular reason to fear typhoid. In camp, thousands of men might draw their water from the same well or stream, and once the bacterium was present it spread quickly through the ranks. The disease could empty a barracks in a matter of weeks. During the Second Boer War in South Africa, which lasted from 1899 to 1902, far more British soldiers died of disease than were killed by enemy action, and typhoid was the most lethal of those diseases. Wright had followed the work of Louis Pasteur, whose vaccines against anthrax and rabies had shown that it was possible to teach the body to resist a microbe before it was encountered, and he was convinced that the same principle could be applied to the typhoid bacillus.

His method was simple in principle. Typhoid bacteria were grown in a warm broth until there were millions of them and then killed by heat, so that they could no longer cause infection while still, Wright hoped, provoking the body's defences. In 1896 he inoculated himself and two of his assistants, and when the experiment produced no harm he began to use the preparation on volunteers. The injections were not pleasant: they frequently caused a sore arm and a bout of fever, which made some who received them reluctant to return for a second dose.

News of the vaccine travelled quickly. Medical officers in India, where typhoid was a constant danger to British troops, adopted it on a considerable scale, and Wright was able to report that inoculated regiments suffered far less from the disease than others. Not everyone was persuaded. The comparisons were not always fair, because the men who volunteered for inoculation were often those with the strongest constitutions, and the vigorous reaction that followed an injection made commanders and ordinary soldiers wary. Official committees in London examined the evidence and concluded that it was not yet conclusive, and the War Office declined to make inoculation compulsory.

A second, fiercer dispute concerned how the case should be judged. Wright measured the success of his vaccine in the laboratory, counting the bacteria that the white cells of inoculated patients were able to engulf, a technique he called the opsonic index. Critics, among them statisticians, replied that no laboratory count could settle the question, and that the only convincing evidence would come from comparing large groups of inoculated and uninoculated men living under identical conditions. Wright, who had little patience with statistical reasoning, regarded this demand as a distraction from the plain facts of the laboratory.

When the First World War broke out in 1914 the argument acquired a new urgency. The threat of typhoid returned with the armies, and the War Office finally agreed to offer inoculation to the army, though on a voluntary basis. Wright, by then the head of a large research department at St Mary's Hospital in London, campaigned publicly for it to be made compulsory, pressing his case with anyone who would listen. Take-up improved as the war went on and typhoid was brought under control, though the improvement owed as much to better sanitation and to the boiling of drinking water as to the vaccine itself.

Wright had moved to St Mary's Hospital in London in 1902 and built up there an Inoculation Department that became one of the most productive medical research centres in Britain. Among the young scientists who passed through it was Alexander Fleming, later the discoverer of penicillin. Wright himself was knighted in 1906 and lived until 1947, long enough to see the vaccine he had pioneered become standard equipment for soldiers.

The vaccine that Wright devised has long since been replaced. The whole-cell preparation caused too many reactions to be used indefinitely, and in the later twentieth century it gave way first to a purified polysaccharide injected vaccine and later to an oral vaccine made from a weakened strain of the bacterium. Yet the principle that Wright established, that a killed bacterium can be used to train the immune system against a living one, remains fundamental, and the difficulties he faced in proving his case, against resistance from the military and from the statisticians, are still familiar to anyone who has tried to introduce a new medical measure.

Among the gifts that nineteenth-century engineers made to public health, one of the simplest is still at work. In 1804 a Scottish bleacher named John Gibb built a bed of sand through which he passed the water supplying his works at Paisley, and in 1829 the Chelsea Waterworks in London began filtering the water it drew from the Thames. The practice spread slowly at first. It was only after the physician John Snow traced a cholera outbreak in Soho to a single contaminated pump in 1854 that the case for cleaning water before it reached the customer became irresistible.

A slow sand filter is essentially a large, shallow basin. Above the bed stands a layer of water perhaps a metre deep, and at the surface of the sand itself, within days of the filter being filled, there forms a thin, sticky mat of algae, bacteria, protozoa and trapped organic particles. German engineers gave this layer the name by which it is still known: the schmutzdecke, or 'dirty layer'.

The sand itself is fine, with grains typically between about a tenth and a third of a millimetre across, and the bed is usually between half a metre and a metre and a half deep. Underneath lie several layers of progressively coarser gravel, which support the sand and allow the water to pass freely, and below them a network of perforated pipes collects the treated water. At the outlet a valve adjusts the speed at which water leaves, and therefore the depth of water standing above the bed.

Water is admitted at the top and moves downwards under gravity, but so slowly that it takes hours to pass through the bed; a typical filter treats only a few tenths of a metre an hour. Three processes remove contaminants. The finest particles are strained out in the narrow spaces between the grains of sand. Many others stick to the surfaces of the grains and to the sticky mat above them, a process known as adsorption. The third process is biological: the mat and the upper sand teem with bacteria, protozoa, rotifers and tiny worms, and these organisms feed on the microbes in the raw water, digesting organic matter and destroying pathogens.

The filter is particularly effective against the organisms that cause waterborne disease. Bacteria such as those responsible for cholera and typhoid are removed in very large numbers, as are the cysts of protozoa such as Giardia and Cryptosporidium, which are resistant to chlorine. The removal of viruses is less dependable, because they are small enough to pass through the spaces between grains, and the process is usually followed by chlorination or ultraviolet treatment where viruses are a concern.

Slow sand filtration differs from the rapid filtration used in most large modern plants. Rapid filters rely on chemicals, added earlier in the process, that make small particles clump into larger ones which can then be caught in a bed of coarse sand at high speed; they also need frequent backwashing with clean water. Slow filters use no chemicals at all, are cheap to run and can be powered by gravity, but they need a large area of land and cannot cope with water that is heavily polluted.

Over weeks or months the mat thickens and the flow slows, and the depth of water above the bed rises. The standard remedy is to drain the filter and scrape off the top centimetre or two of sand with a spade or a machine. The filter must then be left to ripen: the mat re-forms only after a period of days or weeks, during which the water produced is diverted to waste. In a well-run plant this cycle is repeated for years before the sand has to be replaced.

The clearest evidence of what filtration can achieve came from Hamburg in 1892. The city drew its drinking water unfiltered from the river Elbe, while the neighbouring town of Altona, which took water from the same river, passed it through sand. When cholera reached both places that year, Hamburg suffered thousands of deaths and Altona only a few hundred. Later analyses have questioned how far the difference can be attributed to filtration alone, since the two towns differed in other respects too, but the episode helped to persuade cities across Europe and North America to filter their supplies.

Slow sand filters have limits that are less often publicised. Their performance falls in very cold water, when the organisms in the mat become less active, and it is difficult to know how much of the purification should be credited to straining, to adsorption and to biological action. The cysts of Cryptosporidium are removed only partly, and outbreaks of the disease they cause have occurred even where supplies were filtered. Any sudden rise in turbidity, after heavy rain for example, can overload the bed and force operators to shut the filter down.

Despite these drawbacks the technology has not disappeared. Slow sand filters still treat part of the supply of London, where they were installed more than a century ago, and they are used in a number of cities in continental Europe. In rural areas of low-income countries they are attractive because they need no pumps and no chemicals: a gravity-fed unit can serve a small community for decades with little more than occasional scraping. A household version, the biosand filter, scales the same design down to a container the size of a dustbin, filled and refilled by hand.

A visitor from a country where drinking water is scarce might find it strange that wealthy nations sell water in bottles. In most cities of Europe and North America, clean water arrives at the tap at any hour, yet consumers buy it again in plastic, and the trade is now worth well over a hundred billion dollars a year. The bottles are carried, chilled, displayed and thrown away, and the water inside them has often travelled hundreds of kilometres from a spring that its buyers could not find on a map.

The arguments in favour deserve to be stated fairly. Bottled water is convenient, it is consistent in taste, and in an emergency it saves lives: after an earthquake, a flood or the failure of a city's mains, sealed bottles may be the only safe drink available. Some people also drink more water, and fewer sugary drinks, when a bottle is within reach, which is a genuine benefit to health. Public-health bodies have long accepted that bottled water has a place in disaster relief and in places where the supply cannot be trusted.

The environmental objections begin with what the bottle leaves behind. Most bottles are made of PET, a plastic that can be recycled but is recycled in only a fraction of cases; the rest goes to landfill, to incinerators or into rivers and seas, where it fragments into particles that are now found in every ocean. Making the bottles consumes energy, and so do chilling and transporting them, often over long distances. Where the water is drawn from a spring in a dry region, the extraction itself can lower the water table and compete with local needs.

Yet the environmental case is not the whole story, and the claims made about safety deserve scrutiny. In countries with strong regulation, tap water is tested far more frequently than bottled water is, and the results are published; bottled water, by contrast, is often subject to lighter inspection because it is classified as a food. Several surveys have found small fragments of plastic in bottled water, at concentrations that are sometimes higher than in tap water, although what this means for human health is not yet known.

More important is the message that marketing conveys. An advertisement that shows a bottle beside a mountain stream, and says nothing about the water that comes from the tap, implies that public supplies are second-rate. Water companies complain, with some justice, that they spend large sums on treatment and testing while a rival product sells at several hundred times the price of the same volume delivered to a kitchen. The damage is not that people buy water; it is that they come to doubt the water they already pay for.

The question looks different from the perspective of the developing world. Roughly a quarter of the world's population lacks a supply of water that is safe to drink at home, and for them the bottle is not a luxury but an expensive necessity; families in some cities spend a significant share of their income on sachets and bottles.

The industry argues that it is helping to fill a gap that governments have failed to close. Critics reply that the sums spent on bottled water, though large, are nowhere near what would be needed to build and maintain piped systems, and that the presence of the industry may make it easier for governments to postpone that task.

Against all this stands the argument from consumer choice: adults are entitled to buy what they like. Any campaign that singles out a legal, harmless product as a marker of irresponsibility risks treating consumers as children who cannot weigh a price against a preference. This is a real objection, and it is worth noticing that most of those who buy bottled water do so for reasons that are entirely reasonable: they are travelling, they forgot a refillable bottle, they dislike the taste of their local supply, or they simply prefer cold water with a meal.

My own view is that the case against bottled water is strong but narrower than campaigners suggest. Where supplies are unsafe or have broken down, the bottle is a sensible answer, and no one should be lectured for buying one. In rich countries, however, the product's advantages are slight and its costs real, and the most serious of those costs is not the plastic, which a deposit scheme can largely capture, but the habit of mind it encourages. Even so, a ban would be both impractical and unjust. Campaigns that shame individual drinkers are, in my judgement, more likely to harden attitudes than to change them.

What would a sensible policy look like? It would make public water easy to find and pleasant to drink: fountains in parks and stations, refill points in offices and cafes, and clear information about where a city's water comes from and how it is treated. It would require bottles to be returnable, so that the plastic is collected rather than scattered. And it would treat the purchase of a bottle as what it usually is, a convenience rather than a crime. The aim should be to make tap water the obvious choice, not to make bottled water a source of shame.