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The History of Water Purification

"Till taught by pain, men really know not what good water's worth." So said Byron in his book 'Don Juan'. His poetic insight is true. Water is one of the most fundamental needs of survival. Under the best of circumstances, a human cannot live for more than twelve days without water. Under normal circumstances, not more than six. In dire situations, live may give out after only 3 days.

Over 75% of the earth's surface is covered with water. In fact, it has been calculated that if the earth's solid mass were a perfect sphere, water would surround the solid surface to a depth of about 8,000 feet. Therefore it should not be difficult to find water.

The problem is that the human body requires relatively pure water. The hydrologic cycle of evaporation, cloud formation, and precipitation literally rains down an average of about one half an inch of pure water over the entire surface of the earth each week. But water is a universal solvent, so when the rain reaches the surface of the earth it quickly dissolves nearly every substance it comes in contact with, thereby polluting itself in the process.

The human search for pure water supplies must have begun in prehistoric times. Much of that earliest activity is subject to speculation. Some individuals have directed water where they wanted it through trenches dug in the earth. A hollow log may have been used as the first water pipe.

Many years passed before our ancestors learned to build cities and enjoy the convenience of water piped to the home. Our earliest archeological records of central water supply and wastewater disposal date back about 5000 years, to Nippur of Sumeria. In the ruins of Nippur there is an arched drain with each stone being a wedge tapering downward into place. Water was drawn from wells and cisterns. An extensive system of drainage conveyed the wastes from the palaces and residential districts of the city.

The earliest recorded knowledge of water treatment is in the Sanskrit medical lore and Egyptian wall inscriptions. Sanskrit writings dating about 2000 B.C. tell how to purify foul water by boiling in copper vessels, exposure to sunlight, filtering through charcoal, and cooling in an earthen vessel.

There is nothing concerning water treatment in the biblical sanitary and hygienic code of the early Hebrews, although three incidents may be cited as examples of the importance of fresh water. At Morah, Moses is said to have sweetened bitter waters by casting into them a tree shown him by God. During the wandering in the wilderness, the Lord commanded Moses to bring forth water by smiting a rock. At a much later date, Elisha is said to have "healed unto this day" the spring water of Jericho by casting "salt" into it.

The earliest known apparatus for clarifying liquids was pictured on Egyptian walls in the fifteenth and thirteenth centuries B.C. The first picture, in a tomb of the reign of Amenhotep 11 (1447-1420 B.C.), represents the siphoning of either water or settled wine. A second picture, in the tomb of Rameses 11 (1300-1223 B.C.), shows the use of wick siphons in an Egyptian kitchen. In the eighth century A.D., an Arabian alchemist, Geber, wrote a rather specialized dissertation on distillation that included various stills for water and other liquids.

The English philosopher Sir Francis Bacon wrote of his experiments on the purification of water by filtration, boiling, distillation, and clarification by coagulation. This work was published in 1627, one year after his death. Bacon also noted that clarifying water tends to improve health and increase the pleasure of the eye."

The first known illustrated description of sand filters was published in 1685 by Luc Antonio Porzio, an Italian physician. He wrote a book on conserving the health of soldiers in camps, based on his experience in the Austro-Turkish War. This was probably the earliest published work on mass sanitation. He described and illustrated the use of sand filters and sedimentation. Porzio also stated that his filtration method was the same as that of "those who built the Wells in the Palace of the Doges in Venice and in the Palace of Cardinal Sachett, at Rome".

The oldest known archeological examples of water filtration are in Venice and the colonies it occupied. The ornate heads on the cisterns bear dates, but it is not known when the filters were placed. Venice, built on a series of islands, depended on catching and storing rainwater for its principal freshwater supply for over 1300 years. Cisterns were built, and many were connected with sand filters. The rainwater ran off the house tops to the streets, where it was collected in stone-grated catch basins and then filtered through sand into cisterns. The cisterns were usually 10-12 ft deep. The earth was first excavated to the shape of a truncated inverted pyramid. Clay was placed against the sides of the pit. A flat stone was placed in the bottom and a cylindrical wall was built from brick laid with open joints. The space between the clay walls and the central brick cylinder was filled with sand. The stone surfaces of the courtyards were sloped toward the cistern, where perforated stone blocks collected the water at the lowest point and discharged it to the filter sand. This water was always fresh and cool, with a temperature of about 52 degrees F. These cisterns continued to be the principal water supply of Venice until about the sixteenth century.

Many experiments were conducted in the eighteenth and nineteenth centuries in England, France, Germany, and Russia. Henry Darcy patented filters in France and England in 1856 and anticipated all aspects of the American rapid-sand filter except coagulation. He appears to be the first to apply the laws of hydraulics to filter water. The first to supply filtered water to a whole town was completed at Glasgow, Scotland in 1807.

In 1815, on the eve of Waterloo, John Doulton was taken into partnership by the widow Martha Jones who had inherited from her late husband a pottery in Vauxhall Walk, Lambeth, by the side of the Thames. John Doulton founded his first pottery in 1815 at Lambeth, England on the banks of the Thames river. The main products of the original company were ceramic busts, figurines, canning jars and tableware. Influenced by the unrelenting progress of the Industrial Revolution, Doulton placed equal emphasis on industrial applications for ceramic technology. It was John Doulton's son, Henry, however, who carried that tradition of the Lambeth pottery to its zenith.

As early as 1827, Henry Doulton developed ceramic filters for removing bacteria from drinking water. "Offensive to the sight, disgusting to the imagination and destructive to the health." This was how London drinking water, which was drawn from the Thames, was described in a pamphlet published in 1827. The Thames was heavily contaminated with raw sewage; cholera and typhoid epidemics were rampant. The first Doulton¨ water filters were made using various earth and clay materials. By the time Queen Victoria came to the throne, Doulton was established as a manufacturer of domestic and industrial products in a fine stoneware body that bore comparison with any in Europe.

In 1835, Queen Victoria recognized the present health dangers in her drinking water and commissioned Doulton to produce a water filter for the Royal household. Doulton created a gravity fed stoneware filter that combined the technology of a ceramic filter with the artistry of a hand crafted pottery water container. By 1846, the Lambeth factory was in the vanguard of the revolution in sanitation which Chadwick and the great reformers of the day brought to metropolitan England. Without the hard work and foresight of Henry Doulton that revolution would have been best delayed by decades.

Henry Doulton introduced the Doulton¨ Manganous Carbon water filter in 1862, the same year that Louis Pasteur's experiments with bacteria conclusively exploded the myth of Spontaneous Generation and proved that all microorganisms arise from other microorganisms. .

This more advanced understanding of bacteria made it possible to direct Research and Development efforts to the creation of a porous ceramic capable of filtering out these tiny organisms. With Pasteur's advancement in microbiology, Doulton's Research and Development department, headed by Henry Doulton, created micro porous ceramic (diatomaceous earth) cartridges capable of removing bacteria with better than 99% efficiency. These were rapidly adopted by the military, Crown Agents, hospitals, laboratories and domestic users throughout the world. In 1862, Doulton filters shown at the Kensington International Exhibition proudly wore the Royal arms of Queen Victoria.

In 1882 Henry Doulton acquired a small factory in the Midlands, motherland of the Staffordshire potteries and the home of the Doulton Drinking Water Purifier. By 1901, King Edward VII knighted Henry Doulton and in 1902 King Edward VII conferred the double honour of the royal warrant and the specific - as opposed to the assumed - right to use the title "Royal" for his work on drinking water filtration. This Royal Warrant authorized the company to use the word ROYAL in reference to its products. Honors were won at the great international exhibitions at Chicago and Paris and the range of products proliferated. Queen Victoria bestowed upon Doulton the right to embellish each of its units with the ROYAL CREST.

In 1906, Doulton introduced a filter that proved to be equal to the one Louis Pasteur had developed in France. It was rapidly adopted by hospitals, laboratories and for use in domestic water filtration throughout the world. The popularity and effectiveness of even the early 20th century designs has resulted in their continued use in world wide. The range and efficiency of Doulton¨ domestic water filters has been widely extended over the years to meet the demands of increasingly sophisticated uses. Doulton¨ ceramics are now in use in over 150 countries.

In 1985 the British Berkefeld® brand was acquired by Doulton Industrial Products, the manufacturer of Royal Doulton¨ water filters, a company whose name has been synonymous with high quality and reliability since the early years of the twentieth century. Today the British Berkefeld® name is the preferred choice for water purification products in world-wide locations where outbreaks of illness are associated with unreliable water supplies.

Water Contamination in Modern Times

Potential water pollutants are more numerous and varied than you might think. For ease in discussing them, they can be classified as:

Biological Contaminants - These are parasites, bacteria, viruses, or other undesirable living microorganisms that enter the water mainly via human sewage and proliferate to levels that can cause disease when ingested through drinking water.
 
Inorganic Chemicals - Chemicals that occur naturally but have been mined, processed, refined, and concentrated by man, to the point where they have become contaminants. Examples include: cyanide, fluoride, and heavy metals like lead.
 
Radioactive Elements - They exist in nature at low levels, but nuclear power plants and military installations are responsible for adding additional radioactivity, often at higher levels than are found naturally in waterways.
 
Fertilizers - Nitrogen and phosphorous from agricultural fertilizers and sewage are plant nutrients that cause an overabundance of bacteria and algae in lakes when high amounts of this "food" are available. Nitrate (nitrogen) in particular is a potential problem in drinking water.
 
Synthetic Organic Chemicals (SOCs) -Chemists define an organic chemical as one that contains carbon. This can be a bit confusing because many people associate the word "organic" with nature or natural products. This is partly true. Organic chemicals are everywhere in nature, trees, plant life, soils, and in humans. Interaction of these chemicals are the basic processes of life and the life cycle. Synthetic organic chemicals are those which are created by man in the laboratory. The bottom line is that both natural and manmade chemicals contain carbon. However, many of those synthesized by man are dangerous pollutants and have no place or niche in waterways or any other part of the environment. They are foreign to nature and are a serious potential detriment to it, humans included. Seriously damaging health effects have been linked to many SOCs. Examples of familiar SOCs include: industrial solvents, like TCE; pesticides, like DDT; PCBs,- and dioxins.

Characteristics of Water

Several constituents or physical properties of water are also helpful in understanding some aspects of water pollution. A brief discussion of each now will be helpful and act as a point of reference:

Acidity and pH - The pH of water is easily determined by dipping pH paper into the water and observing a color change, or by use of a pH meter in the laboratory. The pH of water will indicate how acidic or alkaline the water is. A pH scale of 0 to 14 is used to indicate the varying degrees of acidity, with 7 being neutral. Anything below 7 is acidic, anything above is alkaline. So the lower the pH, the higher the acidity. Water that is acidic is no problem in itself. The problem is that the more acidic the water, the more corrosive it is. Corrosive water strips household plumbing of metals like lead which can cause serious health effects.
 
Turbidity - Turbid water contains suspended particles to the extent that it becomes cloudy and interferes with the ability of light to pass through the water. The suspended particles associated with turbidity are due to natural silt, clay, soil, decaying vegetation, microorganisms, and industrial waste discharge. One of the main problems with turbidity is the fact that toxic chemicals discharged into waterways often attach to these suspended particles.
 
Hardness - Hard water contains a high amount of calcium, magnesium, or iron in addition to other minerals. Problems with hard water have traditionally been economic or aesthetic, such as the reduction in the cleansing power of soap and the build up of scale in hot water heaters, boilers, and hot water pipes. However, while many seek to remove these minerals by softening their drinking water, an increasing pool of evidence points to the lack of mineral availability as contributing to certain health effects.

Water Quality

Drinking water quality is critically important to good health. Ideally, drinking water should be wholesome, physically attractive, free from all harmful organisms and have a chemical content which will promote the health of the consumer.

The finite amount of water on the planet participates in a recycling scheme that provides for its reuse. This recycling of water is termed the "Hydrologic Cycle".

Energy from the sun causes the evaporation of water from the seas, lakes, rivers and streams. Other sources of water vapor include plant and animal life and combustion.

The evaporated water may condense in clouds as the temperature drops in the upper atmosphere. Winds may transport the water in the clouds over great distances before releasing it in the form of rain, sleet, or snow which falls to the ground.

As the water condenses and falls through the atmosphere, it adsorbs any gases which may be rising from the environment below. This is the principal cause of acid rain and acid snow.

Upon reaching the earth, the water either percolates through the soil to the water table or finds its way to a body of water.

Since water, to some degree, can dissolve every naturally occurring substance on earth, it becomes contaminated with the substances that it contacts ... both in the air and the ground.

Besides carrying dissolved minerals (many of which are beneficial to the consumer), water also carries suspended solids ... including a wide range of living materials including bacteria of all types and fungi (many of which are not beneficial). Water can also carry other liquids ... as an emulsion, in solution, or as a mixture. Many of these foreign liquids are not beneficial to the consumer.

So ... the water you drink, even from your kitchen faucet, may have many contaminants that are not beneficial, and, in some cases, bad for you. In 1993, NBC's television program "DateLine" documented just this fact. Concerns with public water treatment systems in Milwaukee and New York were given as examples of failure to remove potentially deadly organisms from drinking water.

The Berkey® filters have been shown to be capable of removing the specific organism named in the program, Cryptosporidium, from water.1

The following pages deal with some of the contaminants often found in drinking water.

Aluminum

Aluminum occurs naturally in some waters but is also introduced as aluminum sulfate by some Aluminum water departments to remove fine particles, color and bacteria. Municipal water departments usually control the water to a slightly alkaline condition, i.e., pH between 7 and 8. In alkaline conditions aluminum precipitates as fine solid particles, which are then filtered out by means of sand filters. However, sand filters become less efficient for particles as small as 4 to 5 microns and therefore fine particles slip through

For years, researchers have puzzled over the surprisingly high levels of aluminum that turn up in the shriveled brains of Alzheimer's disease victims. While some scientists believe that the aluminum deposits are only a side effect of Alzheimer's, a growing number of investigators say that aluminum. may play a central role in causing the disease that afflicts mostly elderly people.

The latest evidence of a link emerged when Australian scientists reported that aluminum used to purify water accumulated in the brains of laboratory rats. The Australian study focused new interest on the issue at a time when Ottawa's environmental health directorate is preparing to propose Canada's first national guidelines for aluminum levels in drinking water. The Australian study was important, said the directorate's chief, Dr. Barry Thomas, because it showed that aluminum in drinking water can be absorbed by the body. "As to whether it actually causes memory loss and brain damage," added Thomas, "there is not conclusive evidence. But we fear that it may."

Although tiny amounts of aluminum are used in a variety of products, including antacids, antiperspirants, and some processed foods, the metal is pervasively present in drinking water. The reason: municipalities in Canada and other countries often use aluminum sulfate, or alum, to remove mineral particles from water in filtration plants-a process that leaves an aluminum residue in the water.

In the past, studies in Canada and other countries have pointed to links between aluminum and Alzheimer's. University of Toronto researchers found in a 1991 study that they could slow the rate of deterioration in Alzheimer's patients by treating them with a drug that removed some aluminum from their brains.

In a far-reaching study published in January (1995), William Forbes, a university of Waterloo gerontologist, demonstrated an apparent connection between mental impairment and aluminum in about 100 Ontario communities. In each community, researchers determined the amount of aluminum 'in the water supply and tested the mental state of people starting at the age of 45 and continuing over a period of 35 years. They concluded, said Forbes, that the risk of impaired mental functions was "almost 10 times higher in areas where the aluminum. levels in drinking water were high."

Since Berkey® filter elements efficiently filter down to less than I micron; they remove most of the residual aluminum.

Two hundred parts per billion is the maximum level likely to be encountered in our water supply. It is also the maximum allowable level stipulated by the EEC Regulations but the guide level is 50 parts per billion.

Chlorine

Chlorine is added to our drinking water by many municipal water departments to destroy disease causing bacteria. This treatment is essential to prevent widespread epidemics of dangerous diseases. In order to ensure that the water is as sterile as possible right up to the tap, an excess of chlorine usually .5 parts per million (ppm) may be added.

Some of the residual chlorine is consumed on its passage through the distribution main; so the amount of chlorine in our drinking water depends on how close the house is to the water treatment plant.

The residual taste and smell of chlorine is unpleasant and, as it has completed its task by the time it reaches the tap, it can then be removed by a "point of use" carbon filter.

Cryptosporidium

This organic sporozoan, first described in 1907, wasn't recognized as a cause of human illness until 1976. It is a protozoan parasite that can infect a variety of animals.

In the environment, Cryptosporidium exists as a resilient, infectious, round oocyst about six microns in diameter. The oocyst is a "suitcase" for the infectious material inside.

Cryptospofidium is widespread in the environment. Oocysts have been found in rivers, streams, lakes, reservoirs, sewage, and treated surface water. Once introduced to water, the oocyst can survive for weeks, even at low temperatures. The organism has been found in humans, cattle, sheep, swine, goats, cats, and dogs as well as deer, raccoons, foxes, coyotes, beavers, muskrats, rabbits and squirrels. Oocysts infecting certain species can infect another (referred to as cross-transmission). For example, organisms from domestic animals (cattle, dogs, cats, etc.) are able to infect humans. Conversely, organisms from humans can infect animals. Consequently, animals typically found in watersheds may serve as sources of infection. Moreover, infection can occur not only from drinking contaminated water but also from eating contaminated food and from exposure to fecally contaminated environmental surfaces.

When ingested, the Oocysts pass through the stomach into the small intestine. There the Oocysts split open, releasing sporozoites which invade the cells lining the gastrointestinal tract. Infected cells lining the intestine appear normal, but their ability to absorb water and nutrients is severely impaired. The water and food ingested simply passes through the digestive system. Additional Oocysts are formed in the intestine and either split open to release additional sporozoites to continue the infection or excreted in the feces.

The Cryptosporidium infection causes an illness called cryptospopidiosis. After the Oocysts are ingested, the incubation period typically varies from two to 12 days with an average of seven days. Disease symptoms include diarrhea, abdominal cramps, nausea, occasional vomiting and low grade fever.

The number of Oocysts that must be ingested to cause infection in humans isn't known. Studies indicate that as few as ten and perhaps as many as 500 Oocysts are required to initiate infections in mammals. The infectious dose for humans is thought to be fewer than ten.

Cryptosporidiosis typically last 10 to 14 days. However, it may linger off and on for up to 30 days and infrequently can persist for extended periods. Children may be the most susceptible, particularly two- and under. A cure for Cryptospotidiosis has not been found. Recovery depends on the patient's immune system. The disease can be fatal for those with AIDS.

There are two varieties of the oocyst; (1) a sphere of about 4.5 micron 'in diameter and (2) an ellipse of about 7 x 5 micron.

The thick walls of the Oocysts make it difficult, almost impractical, to kill with the UV systems in most domestic water filters. Also, the cyst is much more difficult to kill using chlorine than normal coliform found in drinking water.

Since Super Steraysl? ceramic filter elements are manufactured so that they remove pathogenic bacteria down to I micron in size; they are effective in the removal of Cryptosporidium.

Lead

People, and children in particular, are at risk if they ingest lead ... especially if they are six or younger. Even low lead levels are reported to cause the following types of problems: poor mental performance, low weight at birth, interference with the metabolism of Vitamin D, delayed growth and neurological development, and poor attention span.

Dr. Sue Binder, chief of the lead poisoning branch at the Centers of Disease Control in Atlanta, Georgia, reports, "We see decreased intelligence, hearing problems and smaller stature as a result of lead exposure. Binder says that even moderate levels of exposure can interfere with the ability to pay attention and may play an important role in learning disorders and antisocial behavior. According to some national health experts over 60 million homes are potential lead hazards due to lead-based paints which may disintegrate into dust. Parents in older homes should take steps to clean toys often. Children should be trained to clean their hands before eating and put only food and water into their mouths.

Drinking water may be even more hazardous than the paint dust. The Environmental Protection Agency (EPA) reports that lead in drinking water contributes to about 20% of the total lead exposure for the average citizen. The EPA has also reported that more than 85% of the blood lead detected in bottle-fed infants comes from drinking formula made with lead-bearing water. A Scottish study concluded that the soluble lead levels in water were significantly higher in the home, and in the blood, of retarded children compared to the blood of healthy children.

The EPA has established an 'action' threshold level of 15 parts per billion (ppb), that is, if your drinking water tests at levels exceeding 15 ppb actions should be taken to reduce the levels. This very low threshold shows how toxic lead really is. The problem is compounded by the fact that our senses cannot detect lead at this level . . . you can't smell, taste, or see the lead.

The good news is that the waters in lakes and streams normally do not contain lead. The bad news is that the water distribution system-water mains, service lines, household copper pipe's which have been joined with lead-based solder, and some faucets, may be made, in part, with lead alloys. Homes built before 1930 are likely to have lead pipes. Between 1930 and 1986, most of the homes built used copper pipe and are likely to have lead-solder joints. In 1986, Congress banned the use of solder containing more than 0.2% lead and also set a limit of 8% lead in all faucets, piping, and pipe fittings.

Since you can't detect lead in drinking water by sight, smell, or taste, the only way to be sure that your drinking and cooking water does not exceed the action threshold is to test it. Until your water has been tested, there are some actions that you can take to reduce the risk of ingesting toxic levels of lead. Because the lead content in your drinking water increases with the amount of time that it spends in contact with lead (lead which may be in the pipes, fittings, and/or faucets) lead content is highest in water that's first drawn in the morning. By simply allowing the water to run for a few minutes, the high-lead content water in the lines will be flushed out. It's also a good idea to use only cold water for cooking purposes. The higher the temperature of the water, the higher the rate at which lead leaches into the water.

Organic Chemicals

0rganic chemicals in our drinking water may be naturally occurring or result from agricultural or industrial pollution.

Naturally occurring organics result from the water passing through peat or decaying vegetation before reaching the reservoir. These organics are usually humic acids or tannin, the unpleasant aspects of which are color, taste and odor.

Organics introduced by agricultural or industrial pollution are herbicides, pesticides, and organic solvents. More recently we have learned of the presence of PAHs (Poly Aromatic Hydrocarbons) which are by-products of the decomposition of the bituminous Ifiiing of the water supply i .

Some of these organics have been associated with long term health effects such as cancer. E.P.A. and E.E.C. regulations call for very low maximum allowable levels. Furthermore, the reaction of some of these organics with the residual chlorine in the drinking water can produce chlorinated hydrocarbons which are regarded as more harmful than the original organic.

Organic compounds can be effectively removed by adsorption onto activated carbon.

The cavity of the Super Sterasyl? candle contained granulated activated carbon. Used in a gravity filter applications, the Super Sterasyl? effectively reduces organic compounds in the water.

Suspended Particles

The ceramic element is constructed from an inert naturally occurring material, Kieselguhr, which has a very fine porous structure. The formulation and firing of the ceramic is closely controlled by our Quality Control Department to ensure that the overall size of pores range from 2 to 4.5 microns.

When water passes through the porous ceramic element, Suspended Particles become trapped mainly in the outer layer of pores and only clean water passes through. This principle is similar to that used by municipal water departments when they purify the water supply by passing it through sand filters, although the sand filter has much larger pores than the ceramic element and is therefore much less efficient in the removal of small suspended particles.

Particles of rust, silt, aluminum (see section on aluminum removal) will be trapped on the outer surface of the filter element in normal use and these must be scrubbed off with a brush or scouring pad (3M Scotch-brite or similar) periodically to maintain satisfactory flow through the filter element.

The cleaning frequency will depend on the quality of the water supply but typically, cleaning frequencies of once per month to once every six months would be considered normal.

Various Drinking Water Treatment Methods

There are a number of other drinking water treatment methods used to improve the quality of drinking water other than the technologies used in Berkey® filters. The following is a summary of some of the more popular of those methods:

Activated Carbon

Three forms of activated carbon are used in the treatment of drinking water.

Granulated Activated Carbon

Activated carbon surfaces are both hydrophobic (water hating) and oleophilic (oil loving); that is, they "hate" water but "love" oil. When flow conditions are suitable, dissolved organics in water flowing over the carbon surface "stick" to the carbon in a thin film while the water passes on. This process is call adsorption. All activated carbon, including granulated activated carbon (GAC), has a tremendous surface area resulting from its porous structure.

As a result of the adsorption process, GAC filters are an effective method of removing volatile organic carbon compounds (insecticides and/or pesticides) from drinking water. Uniform, appropriate, flow rate is critical to effective removal of these organic compounds. If flow rate is excessive the residence time is not sufficient for the GAC to remove organic compounds.

While some solid particulate may be removed by GAC filters, normally they are not designed for this purpose. Since GAC filters are not cleanable, water supplies with high solids and/or turbidity can significantly reduce the useful life of GAC filters.

GAC, under quite normal operating conditions, can and do become breeding grounds for bacteria, including pathogenic bacteria. Therefore, steps should be taken to remove any pathogenic bacteria ahead of GAC filtration.

Purchase and installation costs are normally relatively low. Filter element replacement frequency is relatively high.

In most cases, prefiltration, including a ceramic filter element, will improve the effectiveness of the GAC filter.

Carbon Block

Carbon block (CB) filters are an effective method of removing volatile organic carbon compounds (insecticides and/or pesticides) from drinking water.

As with GAC, uniform, appropriate, flow rate is critical to effective removal of these organic compounds. Though CB may impose a higher pressure drop than GAC, it will not form "channels" under the flow pressures normally found in domestic water systems ... which can happen with GAC. When channels form in GAC, supply water can pass through without adequate contact with the carbon surfaces to act on the dissolved organics. Since CB is solid, it cannot "channel."

Solid particulate is removed by CB filters, however, normally they are not designed for this purpose. Since GAC filters are not cleanable, water supplies with high solids and/or turbidity can significantly reduce the useful life of GAC filters.

GAC, under quite normal operating conditions, can and do become breeding grounds for bacteria, including pathogenic bacteria. Therefore, steps should be taken to remove any pathogenic bacteria ahead of GAC filtration.

Purchase and installation costs are normally relatively low. Filter element replacement frequency is relatively high.

In most cases, prefiltration, including a ceramic filter element, will improve the effectiveness of the GAC filter.

Powdered Activated Carbon

Powdered activated carbon (PAC) filters are an effective method of removing volatile organic carbon compounds (insecticides and/or pesticides) from drinking water. As with GAC and CB, uniform, appropriate flow rate is critical to effective removal of these organic compounds.

While solid particulate are removed by PAC filters, normally they are not designed for this purpose. Since PAC filters are not cleanable, water supplies with high so turbidity can significantly reduce the useful life of PAC filters.

PAC, under quite normal operating conditions, can and does become breeding grounds for bacteria, including pathogenic bacteria. Therefore, steps should be taken to remove any pathogenic bacteria ahead of PAC filtration. Purchase and installation costs are relatively low. Filter element replacement frequency is relatively high.

In most cases, prefiltration, including a ceramic filter element, will improve the effectiveness of the PAC filter.

Boiling

Boiling water is an effective method of treating drinking water because very few waterborne diseases are caused by heat resisting organisms. Boiling water for 15 to 20 minutes in an open container will typically disinfect the water and it also drives off any volatile organic compounds.

The disadvantages of boiling are that it wastes water (driven off as steam) and requires energy.

Bromination

Bromine is an oxidizing agent that has been used quite successfully to disinfect swimming pool water. However, it is not normally used to treat drinking water.

Chlorination

Chlorination is used extensively by municipal water treatment plants to disinfect water. However, the gaseous chlorine used by these plants is much too dangerous for home use.

Household bleach (a 5.25% solution of sodium hypochlorite which is equivalent to 5% available chlorine) can be used for disinfecting drinking water. Calcium hypochlorite granules (with about 70% available chlorine) are also available but are not very convenient to use. When chlorine is fed into water, it first reacts with any iron, manganese, or hydrogen sulfide that may be in the water. If any residual (unreacted) chlorine remains, after reacting with these minerals, it will next react with any organic material (including bacteria) present.

The rate of feed of the sodium hypochlorite solution is normally adjusted to make sure that sufficient chlorine is available to fully react with the organics present. When both the mineral and organic reactions have been completed, any residual chlorine remains in the drinking water. Many people find the taste of water with residual chlorine to be objectionable.

Chlorination kills many pathogenic bacteria (including those which cause typhoid, cholera and dysentery). However, cyst forming protozoa which cause amoebic dysentery, and giardiasis are resistant to chlorination.

Home chlorination systems are costly to purchase, operate, and maintain. When properly adjusted to deal effectively with pathogenic bacteria, they leave a taste and odor in the water that many people find objectionable. Contact time and temperature are critical; high flow rates and/or low temperatures reduce the effectiveness of chlorination. Supply water with high pH values may require excessive contact time or solution concentrations. Chlorine can react with organic compounds to form trihalomethane compounds which are known carcinogens.

Distillation

Distillation is usually an effective method of preparing safe drinking water. However, carry overs of volatile organic compounds (herbicides and/or pesticides) may be an issue since they may be evaporated and re-condensed with the water.

Distillation is not normally 'water efficient' and waste water rejected by the system may be significant. Distillation also requires external energy sources; energy costs must be considered. Purchase and installation costs can be significant.

In most cases, pre-filtration, including a ceramic filter element, will improve the effectiveness of a distillation system by improving the quality of supply water (which reduces the waste water rejected from the system).

Iodination

Iodination may be used for emergency treatment of drinking water. Tests show that a 20 exposure to 8.0 ppm of iodine is usually adequate to render water potable ... free from pathogenic bacteria and many viruses. Not enough is yet known about the physiological effects of iodinated water on the human system; however, it is known that high levels of iodine are toxic to humans. For this reason, the use of iodine for drinking water treatment should be considered only for emergency situations.

Ion Exchange

Ion exchange (IEX) systems, such as water softening systems, are effective in the removal of dissolved minerals from the supply water. Waste water rejected by the system and energy costs for operation must be considered when selecting IEX systems. Salt is necessary for regenerating the ion exchange beds. Salt and salt handling costs must be considered. Purchase and installation costs can be significant.

The ion exchange resin in IEX systems may become fouled if the supply water contains significant quantities of suspended particulate or volatile organic compounds. In most cases, pre-filtration, including a ceramic filter element, will improve the effectiveness of a ion exchange system by improving the quality of supply water, which reduces the possibility of any fouling of the ion exchange resin.

Ozone systems

Ozone is a disinfecting agent that can be used in drinking water applications. Because ozone is so active (chemically) it is not possible to maintain an ozone residual in water. Therefore, the most widely used method to produce ozone is electrical (corona) discharge in air or oxygen. Once the ozone is produced, it must be distributed throughout the water to disinfect it. Ozone treatment is generally effective in dealing with pathogenic bacteria and cysts. It does not remove heavy metals, volatile organic chemicals, or chlorine. Ozone systems require external energy sources; energy costs must be considered. Purchase and installation costs can be significant.

Reverse Osmosis

Reverse osmosis (RO) is a membrane filtration process separating dissolved salts from a water stream. In RO, not only are insoluble particles retained by the membrane but also molecules and ions in solution. Concentration of ions near the membrane sets up 'polarization' phenomena which results in an increase in the osmotic pressure of the solution to be treated ... sometimes followed by precipitation. The continuing flow of input water flushes the membrane which removes the ion concentrations and/or precipitates. By subjecting the membrane to pressures on the order of 30 800 p.s.i., 'pure' water is forced through the membrane.

RO is often used to produce fresh water from salt and/or brackish water. In some cases, it is used to concentrate waste.

RO operation requires relatively high pressure on the inlet side to the membrane. External energy, for the pressure pump, is required. Energy costs must be considered when selecting RO as the treatment method. RO systems are not normally 'water efficient' and waste water rejected by the system may be significant. Purchase and installation costs can be significant.

In all cases, prefiltration, including a ceramic filter element, will extend the usefid life of the RO membrane.

Sediment filters

Sediment filters are suitable for the removal of dense and/or large particulate matter and, in some cases, reduction of turbidity. Pleated paper or spun plastic fiber are typical examples of sediment filters. They are not satisfactory performers in the removal of pathogenic bacteria or cysts, heavy metals, pesticides, or insecticides. They cannot be cleaned. These units are usually quite low in cost but filter element replacement frequency is quite high.

In some applications, sediment filters may be used as a prefilter, ahead of a ceramic filter, to reduce cleaning frequency for the ceramic filter.

Ultraviolet

Ultraviolet systems (UV) expose supply water to intense ultraviolet light which kill pathogenic bacteria (cholera, typhoid, salmonella dysenteriae, etc.) and may remove some pathogenic cysts.

The power rating for a UV lamp may be as high as 200 watts. The wavelength of the UV light is normally in the 200300 nm (2,000 3,000 Angstrom units) range. The most efficient microbicidal action is about 250 rim. Water must flow very close to the light source, in a thin layer, and at a uniform, appropriate, flow rate to assure that bacteria are destroyed.

Since any suspended particles (or turbidity) in the water could "shade" bacteria from the direct rays from the UV source, "live" bacteria could pass through the system. For this reason, all UV systems have pre-filtration, often including a ceramic filter element, to assure the effectiveness of the UV system.

UV, by itself, does not remove any particulate matter or turbidity. It does not remove volatile organic compounds such as pesticides or insecticides. External energy is required for operation; energy costs must be considered when selecting UV as the treatment method. Purchase, installation, operating and maintenance costs should be considered before selecting UV as a drinking water treatment system