Chapter 1: Introduction Free

Drinking water or potable water is water that is clean, safe and free from any physical, chemical or biological pollutants. Water is a natural resource and is available freely as almost 70% of earth's surface is filled with water. Therefore, it can be said that drinking water availability is a human birthright. It is indeed fascinating to note that the water that we drink today has always been around in some form or another as it is recycled in the atmosphere and in our glass, which holds water. However, it must be noted that only 2.5% of the global water is freshwater and the remaining part accounts for saline water and the oceans. From this 2.5%, only about 1% is reported to be accessible while the remainder is locked in the form of glaciers and snow.

Overall, experts state that only around 0.007% of the earth's water is available for human consumption. This amount is not sufficient to cater to the needs of the ever-increasing population on our planet. As per the statistics reported by the United Nations, the current world population is almost 7.6 billion and the birth rate is 4.3 every second. The population is expected to reach 8.6 billion by 2030, 9.8 billion in 2050 and almost 11.2 billion in the year 2100. Therefore, it can be clearly seen that the existing water resource will not be able to meet the augmenting water demands of the growing global population. It is important to note that freshwater availability is not globally well distributed due to differences in geographies, climate and environmental factors, industrialization and an upsurge in human activities.

Most of the developing countries face a major shortage of fresh water and in some instances, even if water is available, it may not be safe for human consumption and may also entail long hours of commuting to fetch it from the source. Water is very essential to sustain life and the human body is made up of 70% water. Apart from drinking, water is also needed for basic needs such as bathing, cooking and other domestic chores. According to the United Nations, the water usage rate has increased to more than twice the rate of population growth in the last century. It is very distressing to note that by the year 2025, around 1.8 billion people will be living in water scarce regions and almost two-thirds of the world's population will be living in water strained zones mainly due to uncontrolled and extensive water usage, growth and environmental changes.

Global water regulating bodies such as the United Nations, WHO and institutions working on water quality and health such as UNICEF and many other national and local bodies have been performing a herculean task of monitoring water quality, charting guidelines and organizing programs for public awareness and safety. Over the last several decades, the world has witnessed tremendous progress in water quality management and many goals laid down by the WHO and the UN from time to time like the Millennium Development Goals (MDGs) have been successfully met.

It is very heartening to note that in the year 2015, 71% of the global population (2.6 billion) had been using a safely managed drinking water service since 1990. This implies that they used a water source that was located on the premises and that this source was freely available and free from contamination. This is indeed a huge milestone as the proportion of the global population using an improved drinking water source between 1990 and 2015 has increased from 76% to 91%. Moreover, 89% of the global population used at least a basic service, which is an improved drinking water source that is close to the premise and generally requires a round commuting trip of less than 30 mins.

Although this is a positive result, there are still many milestones to be achieved as the remaining population (663 million) still lack even a basic drinking water service and it is reported that globally at least 2 billion people use a drinking water source that may be contaminated with feces. This is very alarming since the consumption of contaminated water can result in many water borne diseases such as cholera, diarrhea, typhoid and dysentery. It is reported that each day nearly 1000 children die due to preventable water and sanitation related diarrheal diseases. Therefore, after the MDGs, the UN drafted the Sustainable Developmental Goals (SDGs) that cover a set of 17 different objectives and are mainly considered a universal call to action to end poverty, and to protect and ensure that all people enjoy peace and prosperity.

These 17 goals built on the successes of the MDGs and include new areas such as climate change, innovation, sustainable consumption etc. Interestingly, the goals are interconnected and solving one goal will often involve tackling issues related to the other. Goal 6 is ‘clean water and sanitation’ and the salient points related to clean water are that by 2030, universal and equitable access to safe and affordable drinking water should be available for all and by 2030, water quality should be improved by reducing pollution, minimizing the release of hazardous chemicals, having a proportion of untreated waste water and substantially increasing recycling and safe reuse globally. Most importantly, one of the main goals is to expand international cooperation and capacity building support to developing countries in water related activities and programmes including water harvesting, desalination, water efficiency, waste water treatment, recycling and reuse technologies.¹ 

In this book, an attempt has been made to discuss these technologies with respect to their application in developing countries. Yet another global monitoring body is the WHO and UNICEF joint monitoring Programme for water supply, sanitation and hygiene (JMP), which has produced regular reports on the progress of the work related to goal 6, on drinking water, sanitation and hygiene, since 1990. JMP has developed a global database and was responsible for monitoring the progress of the 2015 MDG. It has now been entrusted with the responsibility of monitoring the progress of the 2030 SDG targets related to drinking water, sanitation and hygiene.

Recently, in 2017, JMP released the first update on the first global baseline estimates for the SDG targets related to drinking water. According to this update, the salient conclusion related to drinking water was that there are many people who still lack access to drinking water, especially in the rural areas. Although there are billions of people who have had access to a basic drinking water facility since 2000, these facilities do not provide safe water and the potential risk of consuming contaminated water is significant. Therefore, the risk of contracting water borne diseases is very high, especially among young children who are prone to diseases such as diarrhea, hepatitis, cholera and typhoid.

Yet another key finding in this report is that there are big gaps in services between the urban and rural areas. For instance, it is reported that two out of three people with safe managed drinking water live in urban areas and of the 161 million people who use untreated surface water (from lakes, rivers or irrigation channels), 150 million live in rural areas. This clearly points out that there is a huge requirement to improve access to safe and clean drinking water in the rural regions, which are mainly located in the developing countries across the world. Some of the developing countries are shown in Figure 1.1.

Thus, availability of safe and clean drinking water is the basic right of every individual and all countries globally have the responsibility to ensure that it is provided to all. This is very important in developing countries as the provision of such a basic requirement and improved services related to drinking water will ensure a bright future for the coming generation. Most importantly, enhanced water supply and better management of water resources can boost the economic growth of a country and contribute significantly to poverty reduction.² 

One of the most important aspects to be understood and considered in any water treatment program is the quality of the source water. It is a well-established fact that water can have a plethora of contaminants depending on the origin of water and the pollutants that find their way into water bodies from external sources. These two major contributors to the quality of water can therefore introduce a spectrum of substances that can pose a challenge in water treatment processes. For instance, variations in water compositions can be expected based on whether the raw water being treated is surface or ground water and the geographical region as well. On the other hand, due to extensive industrial and human activities over decades, waste water and sewage may find their way into water bodies thereby majorly contributing to the high level of contaminants in fresh and stored water sources.

Although describing every pollutant in detail is beyond the scope of this book, it is necessary to understand some major classes of pollutants and the health risk they cause when consumed by humans. This information is needed to comprehend the importance of water treatment, especially in the developing countries where the affected population is large in number but the economic conditions are not conducive to sophisticated treatment methods. The following sections describe the major types of pollutants, highlighting the significant ones and the diseases that can be caused in humans when water is consumed without adequate treatment.

Common water pollutants can be classified into physical, chemical and biological varieties. The major classification is given in Figure 1.2. Water usually contains physical, chemical and microbiological contaminants that pollute water and can pose serious health issues to humans. Physical pollutants include increased levels of turbidity in water, which may be due the presence of sediment or organic contaminants present in it. These factors impart an obnoxious odor and color to water thus rendering it aesthetically unacceptable by humans. These physical contaminants may have originated due to other chemical or microbiological sources that will be discussed in the following sections.

Chemical pollutants can get introduced into water from waste water and industrial effluents. These include a spectrum of inorganic contaminants such as Arsenic, lead, Mercury, Fluoride and Chromium and organic contaminants like Acrylamide, Carbon tetrachloride and vinyl chlorides and many others. Radioactive pollutants such as Uranium, and alpha and beta emitters are also reported to be found in water. For eons, chemical disinfection using chlorine, chlorine dioxide and chloramines has been used to treat water and this has been found to remain in residual amounts in treated water. Although residual disinfectants are required to prevent recontamination in water distribution systems, high levels of the same can pose a health hazard.

Disinfection byproducts (DBPs) are yet another class of important chemical contaminant that are routinely present in water if chemical disinfection is used to treat drinking water. They are generally formed due to various chemical reactions that occur between the chemical disinfectant and the organic and inorganic polluting matter found in water. Thus bromate, chlorite and trihalomethanes, which are potential carcinogens, are also deleterious compounds that fall under the class of chemical contaminants as DBPs.

Microbial pollutants form a major class of water contaminants, as they can seriously affect human health. Among the microbial contaminants, bacteria, protozoa and viruses constitute the main types that are commonly found in water. Many of these microorganisms are pathogenic in nature and can cause various diseases in humans. Since it is difficult to detect pathogenic microorganisms due to the time it takes for the analysis and the risk involved in handling such specimens, the concept of indicator microorganisms was introduced. Escherichia coli, fecal coliforms and fecal streptococci are a few indicator microorganisms. The presence of indicator organisms in water indicates that it is indeed polluted and is likely to contain pathogenic species as well.

More information on each class of pollutants is included in the following sections. Emphasis on certain key aspects in each class such as their origin, likely route of entry into water, complications and health risks that occur when they are consumed without appropriate treatment is of paramount importance. Some examples of contaminants with a detailed description are also provided as this forms the foundation based on which the importance of safe, effective and economical water treatment can be understood, especially in the context of developing countries where the risks are huge, and the means are poor.

The colour and odour of drinking water have a huge role to play and substances contributing to colour and odour in potable water systems are referred to as physical pollutants. This is because humans generally accept and consume drinking water based on its appearance, as water that is aesthetically pure and pleasant is generally approved for potable purposes. However, clear, odorless and colourless water does not imply that it is free from other contaminants such as chemical pollutants and microorganisms. Thus, water that is aesthetically unacceptable can lead to the use of water from sources that are aesthetically more acceptable but possibly unsafe for human health. Therefore, taste and odour of drinking water are of paramount importance and should be acceptable to the consumer.

There are several ways by which the colour, odour and taste of drinking water may change thereby leading to its acceptability issues for the end consumers. Natural organic and inorganic matter, chemical and biological contaminants, synthetic chemicals, corrosion of metal pipes and microbial activity during the storage and distribution of potable water are some of the ways that may contribute to colour and taste changes. However, for all practical purposes, the two main factors are chemically derived pollutants and biological contaminants.

Biological pollutants include Actinomycetes and certain fungi, which are usually present on surface water and they produce a substance called ‘goemin’ and 2-methyl isobirneol. These substances can lead to taste and odour problems in water. Certain algae and cyanobacteria also produce similar substances and cyanotoxins, which can aggravate the issue and cause problems in the coagulation and filtration processes that are used in water treatment. Iron bacteria thrive in waters that contain high levels of ferrous and manganese salts and they oxidize these substances to produce rust coloured deposits on the walls of tanks and pipes and this in turn can seep into water. Similarly, invertebrate animals such as crustaceans, snails and zebra mussels can also penetrate filters and storage tanks imparting an unpleasant taste and odour to water.

Myriad chemicals can find their way into water resulting in acceptability issues. For instance, when aluminum is present over 0.1 to 0.2 mg l⁻¹, it generally results in taste issues. Some chemicals such as chlorine are easily detectable in terms of taste and odour even when present at a concentration below 1 mg l⁻¹. The odour threshold of ammonia is around 1.5 mg l⁻¹ and for hydrogen sulphide, it is as low as 0.05 to 0.1 mg l⁻¹ when consumers can sense the rotten egg odour. Other chemicals such as copper generally get into water from leaching of pipes and above 2 mg l⁻¹, copper contributes to colour and taste issues. Colour in water can be due to organic matter such as humic and fluvic acids, iron and other metals, and industrial effluents, and when present above 15 true colour units (TCU), they are detectable visually. Hardness of water due to the presence of calcium and magnesium salts results in precipitation of soap scum and when they are present above 200 mg l⁻¹, they can lead to the deposition of scale in pipes and render water with an unpleasant taste.

Total dissolved solid (TDS) when present in low quantities (less than 600 mg l⁻¹) generally does not pose a problem. However, when the concentration gets elevated to more than 1000 mg l⁻¹, the water becomes unpalatable and results in additional issues such as scaling of pipes and the water distribution system. Yet another important aspect of acceptability of water is its turbidity, which is expressed in terms of nephelometric turbidity units (NTU). Particles such as silt, clay, chemical precipitates and organic impurities contribute to the turbidity of water and when the levels increase to above 4 NTU, it becomes visible and renders the water unacceptable to the end user. It should be less than 0.5 NTU so that the water can be consumed safely. Moreover, augmented levels of turbidity indicate the presence of potential chemical or microbiological contaminants apart from just causing aesthetic issues.³ 

A spectrum of chemical pollutants may be present in drinking water either naturally or introduced due to human and environmental activities. The type of chemical pollutants present is typically dependent on myriad factors such as the water source and storage, geographical region, and possible contamination sites. Most importantly, the type and concentration of the contaminants keep varying and are always in a constant flux. If left untreated, chemical contaminants pose a great threat to humans and therefore they must be identified and subsequently treated appropriately. This becomes of paramount importance in the context of developing countries where the resources and economics of the treatment processes need careful consideration. Over the years, several chemical substances have found their way into raw water such as emerging contaminants like pharmaceutical compounds, fertilizers, pesticides and their derivatives.

Chemical pollutants may be present in the form of inorganic, organic and radioactive contaminants. Often, disinfectants used for water treatment may themselves contribute to the chemical contamination when present in excess quantities. An excess amount of chemical disinfectants is generally used in water treatment schemes to ensure that there is no regrowth of microbes in the distribution system. However, these excess concentrations also react with other organic matter present in the water leading to the formation of disinfection byproducts (DBPs). Most of the chemical pollutants when present at a concentration above the permissible limits laid down by water authorities like the WHO lead to innumerable health hazards in humans. Many of them also contribute to the acceptability issues discussed in the previous section.

Chemical contaminants being innumerable, it is beyond the scope of this book to describe each one in detail. However, some of them along with the health risks associated with their presence in drinking water are described in Table 1.1. Many of them can cause health problems ranging from gastrointestinal disturbances to severe cases of cancer and genotoxicity. Continued efforts by various stakeholders and experts have led to more information on these chemical contaminants and their occurrence in water. Toxicity studies on animal and humans have also thrown light on the potential health hazards, which has helped the national and global regulatory bodies like the WHO to come up with the permissible limits for these chemical pollutants.

New and emerging chemical contaminants in water pose a bigger challenge when coming up with a standard for these pollutants. One such chemical contaminant is methyl tertiary butyl ether (MTBE), which is employed as a fuel additive in the United States. This is primarily done to diminish carbon monoxide and curb ozone depletion triggered by automobile emissions of hydrocarbons. Generally, MTBE is detected at a very low concentration of a few nanograms to micrograms in ground water. However, when present at elevated levels, MTBE can be harmful. Studies indicate that MTBE is a rodent carcinogen at high levels, but it is not genotoxic. The studies carried out to date have not come up with conclusive evidence to point out the possible human carcinogenic nature of MTBE. Therefore, the regulation authorities have not yet come up with the permissible limits for MTBE and efforts on this front are in progress.

One of the greatest risks to human health is the presence of microbial contaminants in drinking water. This is because these pollutants can cause severe illness, which can sometimes be fatal. Therefore, this class of pollutants is very important and adequate measures must be taken to avoid drinking microbially contaminated water. Microbes can enter a water body by various ways such as untreated industrial effluents, sewage inflow and other human activities contaminating the water source. Thus, the source water should be kept clean by preventing pollution as far as possible and proper selection of treatment methods and their operation must be carried out to keep these microbes in check. Moreover, the distribution systems should also be monitored, and adequate care should be taken to prevent microbial contamination in the distribution network.

These three aspects, i.e. source water, treatment method and distribution systems, are of paramount importance as any breach in any/all of these can result in a major disease outbreak that can even prove to be fatal to humans. This can be associated with the typical nature of the microbial pollutants that makes them different from the physical and chemical pollutants discussed in the preceding sections. Some of these features are due to the fact that many microbes are pathogenic and can cause acute or chronic diseases, they can aggregate with other suspended particles in water and their concentration can vary in time.

The possibility of acquiring an infection from a pathogenic microorganism present in water depends on a plethora of factors such as the virulence of the pathogen, its concentration in water and its ability to invade the host (human body), which in turn also depends on the immune status of the individual. Once the microbes invade the human body, they multiply and cause acute or chronic conditions that could be mild to severe. It is interesting to note that these waterborne pathogens are also capable of multiplying in food and beverages and can thrive in warm water systems like the Legionella species (Table 1.2), thereby increasing the possibility of infections in humans.

Microbial pollutants can be of various types such as bacteria, viruses, protozoa and helminths, each of which has myriad members exhibiting varying degrees of pathogenicity. Some of these are described in Table 1.2. It is interesting to note that not all microorganisms infecting humans through the fecal-oral route are transmitted only via water. In fact, contamination of food, beverages, unclean hands, and utensils and general poor hygienic conditions of the person and the household are equally responsible for the spread of microbial infections. Moreover, it is important to note that the route of infection cannot be restricted only through drinking contaminated water. Aerosols that contain tiny droplets of water with microbes may also lead to health risks if inhaled by a person, for instance from a shower while bathing. Even cuts, wounds and abrasions of the skin if kept uncovered can be open to invasive microorganisms present in water.

Among the different microbial pollutants that are usually present in contaminated water, bacteria form an important and major class that need careful attention. Most of the bacterial species are ingested while drinking water and they enter the gastrointestinal tract of humans and cause various acute and chronic infections. Subsequently, they get excreted into the feces of the infected humans or animals. A similar route may be observed with viruses such as enteric virus, which affects the gastrointestinal systems of humans, leading to acute and chronic infections. Some viruses that cause respiratory infections in humans can spread through respiratory droplets, which may also be excreted in the feces of the infected person. This shows that the pattern and route of infection can be varied for different microbial pollutants and their sub types.

One of the most common causes of disease and infections due to contaminated water is the presence of protozoa. This is considered to have a major public health and socioeconomic impact and is a major concern worldwide. For instance, cryptosporidiosis is an infection caused by Cryptosporidium species that are present in drinking water. This is a major issue faced by many parts of the world. The main challenge in treating water containing protozoa is the presence of oocysts, cysts and eggs, which are often resistant to typical disinfectants that are used, and, in some instances, they may be difficult to remove by filtration processes too.

Yet another type of pollutant is the helminths or worms such as roundworms, flatworms and hookworms, which are a common source of infection in humans and animals globally. Some of these are transmitted through contaminated water or are associated with using untreated waste water for agriculture. For example, Dracunculus medinensis, commonly known as “guinea worm”, is the only nematode associated with significant transmission by drinking water. Guinea worm infections are generally found in countries of sub-Saharan Africa. The only source of this infection appears to be drinking water, containing infected cyclops, and it is often prevalent in rural areas where piped water may not be available.³ 

Over the last few decades, with increasing industrialization and human and anthropological activities, several classes of pollutants have been found in drinking water. Most of these contaminants are discussed in the earlier section. However, there are innumerable pollutants, still present in drinking water, that usually do not fall in the categories of physical, chemical or microbial pollutants. These substances are called “emerging contaminants” and pose an equal challenge as the other pollutants in drinking water treatment. Typically, they are denoted as Contaminants of emerging concern (CECs) by the Environmental Protection Agency (EPA) and they include pharmaceuticals and personal care products (PPCPs).

The PPCPs are often found in surface waters in low concentration and they may have a detrimental effect on the marine life. Most of the drugs that are taken orally pass through the human body and are excreted and finally may find their way into the water supply, especially if there are possibilities of sewage contamination. Similarly, personal care products such as soaps, fragrances and cosmetics also land up in the water supply. Many of these substances are known to act as endocrine disruptors (EDCs). EDCs are compounds that change the normal functions of hormones, resulting in myriad heath issues such as altered reproductive effects in aquatic organisms. They may be toxic, leading to severe acute toxicity issues. Since these EDCs are different in nature, conventional testing procedures that are adopted for other pollutants may not be sufficient to detect these compounds.

Owing to this challenge, the EPA developed a document titled ‘White Paper Aquatic Life Criteria for Contaminants of Emerging Concern: Part I Challenges and Recommendations’ that outlines the technical issues and recommendations that can be used to modify the existing guidelines. This was primarily published to address the emerging contaminants and come up with a better-quality criterion for drinking water with the current resources and knowledge available.  Emerging contaminants are important due to the risk they may pose to human health and the environment, which has not been fully elucidated yet. Globally, trace amounts of these emerging contaminants are being detected in the water supply in many regions and the EPA is working towards enhancing its understanding of these pollutants.⁴ 

Several experts worldwide are investigating the concentration, types, fate, behaviors and toxicity levels of these emerging contaminants and reports from such studies clearly point out that there is a dearth of published health risk standards for the emerging contaminants that can provide a suitable guideline in treating them. Moreover, several new emerging contaminants are being introduced into the environment and therefore into drinking water that have not yet been detected. Therefore, superior detection methods and treatment technologies are needed in the years to come to detect and remove these contaminants from potable water systems, and at the same time, appropriate measures to prevent the introduction of new contaminants are the need of the hour.

Drinking water should be safe and clean when it reaches the end user, and to ensure this, it is necessary to have water quality guidelines in place so that the water quality can be compared with these guidelines before it is consumed. The World Health Organization (WHO) has played the pivotal role of setting the water quality guidelines, which have been considered the standard for ascertaining drinking water quality globally. As per these guidelines, safe drinking water may be defined as water that does not cause any significant health risk to the end user over the lifetime of consumption.

The WHO guidelines are mainly used to support the development and implementation of different risk management methods that ensure safe drinking water supplies do not contain any hazardous constituents that may pose a health issue. These guidelines were mainly envisioned to provide a scientific basis for the development of various national and regional standards worldwide. Moreover, the WHO guidelines describe the minimum requirement of safe practice to provide safe and clean water to the consumers and most importantly, these guidelines state the numerical guideline values for different acceptable and unacceptable constituents present in water.

It is important to understand that there are no unique drinking water standards that are universally applicable in all countries globally. This is mainly because the needs and capacities of water treatment of one country may vary significantly and the approach of one country or region towards drinking water standards may not necessarily translate to another country or region. This is one of the main reasons for not encouraging the implementation of international standards for drinking water quality. The purpose of the WHO guidelines is to enable countries and regions to form national and regional drinking water standards that can be readily implemented in the respective regions and protect public health.

For instance, the WHO guidelines broadly describe and state that the greatest microbial risk is due to the consumption of water that is contaminated with feces from human or animals/birds, since a plethora of pathogenic bacteria, viruses, protozoa and helminths can find their way into the human body through contaminated water. Therefore, control of microbial contamination should be the prime goal and must never be neglected by water authorities. Chemical contaminants, on the other hand, usually lead to a health threat only after prolonged periods of exposure. Yet another important aspect of water treatment stated in the WHO guidelines is that disinfection should never be compromised when endeavoring to control disinfection byproducts.

Important pointers such as these can be easily adopted by different countries and regions worldwide while preparing the national and regional drinking water standards. A preventative integrated management approach that ensures cooperation from all agencies and stakeholders is the best method to ensure drinking water safety. This will ensure that the quality and safety of the potable water produced are comparable with the WHO standards and at the same time compatible with the local guidelines as the water source, its constituents, treatments methods and needs of the consumers vary from one place to another.

For example, in the US, the safe drinking water act (SDWA) is the main central law that safeguards the drinking water quality and under this law, the Environmental Protection Agency (EPA) sets the drinking water quality standards. This is done by setting the limits for several contaminants routinely found in drinking water. These limits are usually based on the levels that protect human health and should be achievable by employing the best available water treatment technology. Additionally, the water quality testing methods and the time intervals to schedule these tests are also decided by the EPA. It also supervises the states, regions and various water providers who implement those standards. Some examples of pollutants and their limits as per the EPA are listed in Table 1.3.

It is evident from the previous discussions on the spectrum of pollutants that contaminated source water can lead to various health issues. This is especially a major challenge in rural regions of developing countries as there are higher chances of contamination due to poor sanitation and hygiene practices and the low socio-economic conditions. It is well established that fecal contamination of water supplies prevails in many rural regions of developing countries. Over 2 million infections per year that cause almost 600 000 deaths primarily in developing countries are reported by the WHO.

Among the potential diseases due to contaminated drinking water that particularly affect developing countries are bacterial infections due to Shigella species that can be triggered even by a low count of 10 to 100 organisms. Similarly, enteropathogenic E. coli infections are also known to occur in developing countries with infants being affected the most. Viruses such as Hepatitis A virus and protozoa such as Blastocystis hominis are probably the most common pathogens found in water sources in developing countries owing to the poor hygienic conditions. Similarly, Schistosomiasis, which is caused by parasitic worms (e.g. Schistosoma mansoni), is also a great public health concern globally especially in developing countries where it is endemic.

Due to these factors that cause human health hazards that can even be fatal, safe and clean drinking water is of paramount importance. One way to ensure this is preventing contamination of the source water so that the raw water is clean and its quality is within the desirable WHO or the respective National standards. However, this is not always possible as most of the time, especially in developing countries, contamination of the source water occurs by mixing of sewage water and due to general poor hygiene and sanitation around the drinking water source/storage. In some cases, waste water from industrial effluents and domestic waste can lead to the introduction of undesirable and deleterious pollutants. Therefore, water treatment is the only option to ensure safe drinking water.

Drinking water treatment is the main solution that can inactivate or eliminate the various types of pollutants that may be present in the raw water. Any water treatment method will involve one or more steps to remove the pollutants and render the water clean and fit for consumption. Generally, pre-treatment such as flocculation, sedimentation and pre-filtration is carried out, which removes most of the coarse particles and turbidity that may be routinely found in water. Subsequently, different treatment methodologies such as filtration by sand, membranes, ceramics or activated charcoal, and exposure to UV or solar irradiation may be used depending on the source water quality and the required end use. If microbial pollutants are present in the source water, disinfection is of prime importance.

Disinfection, as the name suggests, is the inactivation and/or removal of pathogenic microorganisms from contaminated water. This is especially important when the surface or groundwater is subjected to fecal contamination. Disinfection may be physical, chemical or hybrid in nature and most commonly, the latter is used. Chemical agents such as chlorine and ozone are routinely used in water treatment to kill the infectious microbes that may be present. These chemical disinfectants may not necessarily inactivate all the microbes, e.g. chlorine may not be as effective on Protozoans like Cryptosporidium and some viruses. It is also important to understand that the disinfectants may not be very effective if the source water is highly turbid and when the microbes are surrounded by particulate matter leading to clumping and the formation of agglomerates.

Moreover, chemical disinfectants are known to form disinfection byproducts due to their reaction with organic matter present in the source water. Many disinfection byproducts like Trihalomethanes are potentially carcinogenic and may lead to health risks, if present in excess amounts in the final disinfected water. However, it is necessary to reemphasize here that at no point should the disinfection of water be compromised for the sake of the potential formation of disinfection byproducts. Chemical disinfection of only the source water may not be enough to make the water completely safe as contamination maybe reintroduced in the piping systems and distribution networks. Therefore, some amount of residual chemical disinfectants is added to ensure the safety of drinking water when it reaches the consumer. Needless to say, storage vessels used by the end user and source water protection are also required to ensure that the drinking water is free of contamination.

Water treatment in developing countries is generally carried out by using low cost methods that are easy to operate, involves the use of locally available materials and is feasible either at the point of use at household level or at a community or larger scale level as the case may be. Disinfection in developing countries primarily depends on the use of chemical disinfectants such as commercially available bleach or a sodium hypochloride solution. This is attributed to the fact that it is easily available, relatively safe to handle, inexpensive and easy to apply even at the household level. Therefore, techniques such as UV disinfection are not generally useful for rural set-ups in developing countries due to the need for reliable electricity, cost of the UV set-up and its maintenance requirement.

Thus, based on the previous discussion, the need for clean and safe water, on one hand, and the possibility of various physical, chemical and biological pollutants that may be present in the source water cannot be overstated. Therefore, drinking water treatment techniques play a pivotal role globally, especially in developing countries. This is the main focus of this book and an attempt has been made to cover most of these aspects to highlight the current scenario globally. The following section gives a brief overview of what this book has to offer.

As the title of this book and the preceding sections of this chapter suggest, the focus of this book is elaborating various drinking water treatments for removing or eliminating different pollutants present in source water that are well suited for developing countries. Based on this, each chapter deals with a topic leading to conclusions on this topic. Chapter 2 deals with drinking water treatment techniques that are feasible in rural set-ups. It includes descriptions of and discussion on some of the simple yet effective and economical technologies that have been conventionally used. Novel and upcoming methods that are evolving around the globe to cater to the ever-increasing potable water needs are also highlighted. It will indeed be interesting to find out more about individual and collective efforts from various stakeholders including research scientists and experts in the field of water that have immensely contributed to ensuring safe and clean drinking water is accessible to the remotest areas worldwide.

In a very different yet fascinating way, Chapter 3 will throw light on a simple and beautiful way of conserving water by collecting rain water, which is a gift of nature. Techniques of using the harvested water after appropriate treatment for potable and domestic purposes will clearly show how humans can make efforts to save and use rain water effectively. Along similar lines, Chapter 4 will reveal fascinating ways of reusing waste water after treatment for potable and non-potable purposes. This methodology of conservation of water for reuse is where the world is headed and will form one of the major ways of ensuring safe and clean water for humankind in the decades to come.

As the heart of this book is on drinking water treatment, the explanation of any technique would be incomplete without appropriate examples. Thus, Chapter 5 illustrates a few of the treatment methods described in this book by way of specific case studies. These case studies are included essentially to demonstrate the economic application of the said water treatment techniques in rural scenarios of developing countries. The success of these methodologies as depicted in the case studies gives a ray of hope for the brilliant possibilities for providing safe and clean drinking water to the rural regions of even low-income countries.

For any book that involves discussion on a plethora of water treatment techniques for myriad pollutants that may be present in water, a comparison of the same is of utmost importance. Therefore, Chapter 6 reveals to the reader the best possible treatment method for any contaminant in a developing country scenario. In other words, the methods described in this book will be compared with respect to efficiency in pollutant elimination or inactivation, cost, scalability and overall feasibility and ease of deploying in developing countries. Chapter 7 will essentially wrap up the entire book in a nutshell and include a summary, conclusions and future recommendations drawn based on all the previous chapters.