New Filter Promises Clean Water for Millions

A An ingenious invention is set to bring clean water to the third world, and while the science may be cutting edge, the materials are extremely down to earth. A handful of clay, yesterday’s coffee grounds and some cow manure are the ingredients that could bring clean, safe drinking water to much of the third world.

B The simple new technology, developed by ANU materials scientist Mr Tony Flynn, allows water filters to be made from commonly available materials and fired on the ground using cow manure as the source of heat, without the need for a kiln. The filters have been tested and shown to remove common pathogens, or disease-producing organisms, including E-coli. Unlike other water-filtering devices, the filters are simple and inexpensive to make. "They are very simple to explain and demonstrate and can be made by anyone, anywhere," says Mr Flynn. "They don’t require any Western technology. All you need is terracotta clay, a compliant cow and a match."

C The production of the filters is extremely simple. Take a handful of dry, crushed clay, mix it with a handful of organic material, such as used tea leaves, coffee grounds or rice hulls, add enough water to make a stiff biscuit-like mixture and form a cylindrical pot that has one end closed, then dry it in the sun. According to Mr Flynn, used coffee grounds have given the best results to date. Next, surround the pots with straw; put them in a mound of cow manure, light the straw and then top up the burning manure as required. In less than 60 minutes, the filters are finished. The walls of the finished pot should be about as thick as an adult’s index finger. The properties of cow manure are vital, as the fuel can reach a temperature of 700 degrees in half an hour and will be up to 950 degrees after another 20 to 30 minutes. The manure makes a good fuel because it is very high in organic material that burns readily and quickly. The manure has to be dry and is best used exactly as found in the field; there is no need to break it up or process it any further.

D "A potter’s kiln is an expensive item and could take up to four or five hours to get up to 800 degrees. It needs expensive or scarce fuel, such as gas or wood, to heat it and experience to run it. With no technology, no insulation and nothing other than a pile of cow manure and a match, none of these restrictions apply," Mr Flynn says.

E It is also helpful that, like terracotta clay and organic material, cow dung is freely available across the developing world. "A cow is a natural fuel factory. My understanding is that cow dung as a fuel would be pretty much the same wherever you would find it." Just as using manure as a fuel for domestic uses is not a new idea, the porosity of clay is something that potters have known about for years, and something that, as a former ceramics lecturer in the ANU School of Art, Mr Flynn is well aware of. The difference is that rather than viewing the porous nature of the material as a problem, his filters capitalise on this property. After all, not many people want a pot that will not hold water.

F Other commercial ceramic filters do exist, but, even if available, with prices starting at US$5 each, they are often outside the budgets of most people in the developing world. The filtration process is simple, but effective. The basic principle is that there are passages through the filter that are wide enough for water droplets to pass through, but too narrow for pathogens. Tests with the deadly E-coli bacterium have seen the filters remove 96.4 to 99.8 per cent of the pathogen, well within safe levels. Using only one filter, it takes two hours to filter a litre of water. The use of organic material, which burns away after firing, helps produce the structure in which pathogens will become trapped. It overcomes the potential problems of finer clays that may not let water through and also means that cracks are soon halted. Like clay and cow dung, it is universally available.

G The invention was born out of a World Vision project involving the Manatuto community in East Timor. The charity wanted to help set up a small industry manufacturing water filters, but initial research found the local clay to be too fine, a problem solved by the addition of organic material. While the problems of producing a working ceramic filter in East Timor were overcome, the solution was kiln-based and particular to that community’s materials and could not be applied elsewhere. Manure firing, with no requirement for a kiln, has made this zero-technology approach available anywhere it is needed. With all the components being widely available, Mr Flynn says there is no reason the technology could not be applied throughout the developing world, and with no plans to patent his idea, there will be no legal obstacles to it being adopted in any community that needs it. "Everyone has a right to clean water. These filters have the potential to enable anyone in the world to drink water safely," says Mr Flynn.

The Cause of Linguistic Change

A The changes that have caused the most disagreement are those in pronunciation. We have various sources of evidence for the pronunciations of earlier times, such as spellings, the treatment of words borrowed from other languages or borrowed by them, the descriptions of contemporary grammarians and spelling reformers, and modern pronunciations in all the languages and dialects concerned. From the middle of the sixteenth century onwards, there were writers in England who attempted to describe the positions of the speech organs used in the production of English phonemes and who invented what were, in effect, systems of phonetic symbols. These various kinds of evidence, combined with a knowledge of the mechanisms of speech production, can often give us a very good idea of the pronunciation of an earlier age, though absolute certainty is never possible.

B When we study the pronunciation of a language over any period of a few generations or more, we find that there are always large-scale regularities in the changes. For example, over a certain period of time, just about all the long [aː] vowels in a language may change into long [eː] vowels, or all the [b] consonants in a certain position, for example at the end of a word, may change into [p] consonants. Such regular changes are often called sound laws. There are no universal sound laws, even though sound laws often reflect universal tendencies, but simply particular sound laws for one given language, or dialect, at one given period.

C It is also possible that fashion plays a part in the process of change. It certainly plays a part in the spread of change: one person imitates another, and people with the most prestige are most likely to be imitated, so that a change that takes place in one social group may be imitated, more or less accurately, by speakers in another group. When a social group goes up or down in the world, its pronunciation may gain or lose prestige. A pronunciation of Russian which had formerly been considered desirable became, on the contrary, an undesirable kind of accent to have, so people tried to disguise it. Some of the changes in accepted English pronunciation in the seventeenth and eighteenth centuries have been shown to consist of the replacement of one style of pronunciation by another style that already existed. It is likely that such substitutions were a result of the great social changes of the period: the increased power and wealth of the middle classes, and their steady infiltration upwards into the ranks of the landed gentry, probably carried elements of middle-class pronunciation into upper-class speech.

D A less specific variant of the argument is that children’s imitation is imperfect: they copy their parents’ speech but never reproduce it exactly. This is true, but it is also true that such deviations from adult speech are usually corrected in later childhood. Perhaps it is more significant that even adults show a certain amount of random variation in their pronunciation of a given phoneme, even if the phonetic context is kept unchanged. This, however, cannot explain changes in pronunciation unless it can be shown that there is some systematic trend in the failures of imitation. If they are merely random deviations, they will cancel one another out, and there will be no net change in the language.

E One such force which is often invoked is the principle of ease, or minimisation of effort. The change from fussy to fuzzy would be an example of assimilation, which is a very common kind of change. Assimilation is the changing of a sound under the influence of a neighbouring one. For example, the word scant was once skamt, but the /m/ changed to /n/ under the influence of the following /t/. Greater efficiency has thereby been achieved because /n/ and /t/ are articulated in the same place, with the tip of the tongue against the teeth ridge, whereas /m/ is articulated elsewhere, with the two lips. Thus, the place of articulation of the nasal consonant has been changed to conform with that of the following plosive. A more recent example of the same kind of change is the common pronunciation of football as foopball.

F Assimilation is not the only way in which we change our pronunciation in order to increase efficiency. It is very common for consonants to be lost at the end of a word. In Middle English, word-final [-n] was often lost in unstressed syllables, so that baken, meaning "to bake", changed from [ˈbaːkən] to [ˈbaːkə], and later to [baːk]. Consonant clusters are often simplified. At one time, there was a [t] in words like castle and Christmas, and an initial [k] in words like knight and know. Sometimes, a whole syllable is dropped when two successive syllables begin with the same consonant, a process known as haplology. A recent example is temporary, which in Britain is often pronounced as if it were tempory.