Drinking Water Quality

Safe drinking water is a basic human necessity, a prerequisite to the survival of human race. The quality of drinking water is very important, for, the absence of safe drinking water could result in various waterborne diseases, posing a serious threat to human health, increasing mortality rates. Since water is an excellent solvent, it can easily absorb various microbial and chemical contaminants. Hence, it is absolutely mandatory to effectively monitor, regulate and manage the sources, supply and distribution of drinking water, so that the highest safety levels and aesthetic quality can be assured to the consumers. While scarcity of safe drinking water is primarily an obstacle in the developing countries, causing epic deaths, episodes of outbreaks of waterborne diseases, resulting in high mortality rates have been witnessed in the developed countries, as well. Accessibility to safe drinking water is a relevant concern for countries and continents, across the globe. To this end, the World Health Organization (WHO) has formulated guidelines for countries across the world, regarding drinking water quality. It recommends the assessment of risk factors associated with the presence of physical, chemical, microbial and radiological contaminants in drinking water, with the ultimate goal of effectively managing/controlling drinking water quality, and protecting human health from water borne diseases. The process is facilitated by documentation, management, regulation, and monitoring of the source- supply-distribution chains, along with instructions on proper handling of drinking water. This, in turn, guarantees safe drinking water to end-users, in accordance with the guideline values outlined by the WHO. The recommendations of WHO are flexible enough to accommodate country-specific socio-economic, cultural and environmental variations.


The WHO guidelines on drinking water quality

Since drinking water quality has an important bearing upon human health, the WHO has formulated effective guidelines towards this end, for protecting human life, through assessment and control of risk factors associated with contaminants present in drinking water. Waterborne diseases, such as diarrhea, dysentery, cholera, typhoid and jaundice claim millions of life, every year. The WHO guidelines are aimed towards preventing these life-threatening diseases, by providing structural standards for eliminating/reducing potential risk factors for human health. The scheme for enhancing the quality of drinking water involves plans to be implemented by national governments, based on a comprehensive assessment of health-related risk factors. These plans are known as water safety plans, charted out to ensure adequate supply of safe and aesthetically acceptable drinking water to people around the world. These plans involve plotting the system of water supply by the supplier, hazard identification and risk-assessment from the source of supply to the end-users. The next steps for ensuring the provision of safe drinking water involve execution of improvements required in the supply and distribution system. Monitoring plus verifying the drinking water quality throughout the supply and distribution chains and ensuring that substantial precautionary measures have been undertaken, to protect human health against waterborne diseases are important part of the plan. Regular audits to review the safety levels of drinking water, and developing a resource base through training, are an integral part of the water safety plan. Equally relevant is the documentation of existing practices, establishing channels of communication and management of the state of affairs in the water supply system. Alongside, there is the provision in the guidelines for a comprehensive surveillance of drinking water quality by independent regulators, set up for this purpose. The guidelines aim at long-term improvement in drinking water quality rather than temporary solutions through piecemeal treatments.

Enhancing drinking water quality: periodic reviews and implementation of the WHO guidelines

The WHO recommendations are used by developing and developed countries alike, as the framework for enhancing the safety and aesthetic quality of drinking water. The guidelines are used by national policy makers, health regulators and autonomous agencies for ensuring safe drinking water to their consumers. It is a valuable resource for information on acceptable upper limit values for various chemical and microbial constituents, present in water. The guidelines also establish the paradigm for management techniques associated with risk assessment and the supply cum distribution of safe drinking water. The drinking water quality guidelines followed by Australia, USA and Canada are in congruence with the WHO guidelines. Japan and European Union use the WHO drinking water quality guidelines, as part of their national standard. The WHO guidelines are used by the developing countries as a point of reference, in the absence of well-established directives or national standards for water safety. This pattern clearly demonstrates the awareness among the nations of the world, regarding the profound connection between safe drinking water and human health. This understanding, in turn, has accelerated the pace of development of management and surveillance techniques, for supply and distribution of safe drinking water. The WHO conducts periodic revisions of its guidelines to incorporate changes brought about by a dynamic technological and physical environment. Safety measures for identification and elimination of microbial threats and chemical hazards are implemented, following the WHO guideline values. Also, the functions and extent of involvement of public and private agencies are outlined, including community participation. Scientific innovations on safe levels of chemicals and disease bearing pathogens, found in water, are integrated into the rolling revisions of the guidelines. Periodic reviews also include the ever-increasing/changing modes of supply of water, apart from the conspicuous piped-water supply. Treatment options at the household level to ensure the safety of drinking water is also delineated.

Risk assessment based on physical and chemical quality of drinking water

Physical characteristics of drinking water determine its aesthetic quality and affect the consumer perceptions of its purity and safety. Physical quality of drinking water involves its color, taste, odor, acidity or alkalinity, dissolved solids, temperature, hardness or softness, among others. Along with this, the potency of water to corrode or tarnish the pipelines and household fixtures affect consumer perception about the physical quality of drinking water. Physical quality does not directly pose a threat to human health, but the appearance of water determines whether it is aesthetically agreeable to the end-users, and pleasant enough for consumption. The WHO recommendation values for physical quality is not absolute, for, the aesthetic acceptability of drinking water is an objective judgment. Chemical constituents may be found to exist naturally in sources of water, or may be spilled into water as agricultural or industrial runoffs, as residues of fertilizers, pesticides or industrial pollutants. Chemical constituents such as copper, lead or nickel, are present in faucets, pipes and fixtures of households. Higher than WHO guideline values of lead concentrations in drinking water, may impact the development of nervous system and the renal system. Higher than recommended levels of copper in drinking water, may lead to gastrointestinal diseases and impact the kidney, in cases of long-standing exposure. In some instances, chemical constituents also leak into water through inefficient waste disposal systems practiced by households or hospitals, as also by discharge from treated sewage. The treatment of water for disinfection creates by-products, which may contaminate drinking water. The WHO guideline values, based on hazard identification, provide safe upper limits for chemicals that may be ingested through drinking water, so that there is no significant health implication. The guideline values, however, provide for the leeway to accommodate changes according to the sources of water, proportion/ presence of various chemicals, according to variations, in different geographical settings, around the world. The most commonly found naturally-occurring chemicals in drinking water are fluoride and arsenic. Arsenic is noted to be a highly toxic chemical. The guideline value for arsenic is 0.01 mg /l. higher concentration of arsenic in drinking water could result in severe ailments of the skin including hyper/hypo pigmentation. It could also lead to chronic diseases such as skin cancer, cardio-vascular diseases in children, as also carcinoma of the lungs, urinary bladder and kidney, with prolonged exposure to high concentrations of arsenic in water. Whereas, the presence of fluoride in drinking water till the guideline value of 1.5mg/l is safe, protecting against dental caries, higher concentrations of fluoride may lead to dental fluorosis. More elevated levels of fluoride could result in skeletal damage, and lead to the medical condition of skeletal fluorosis. Typically concentrations around 6mg/ l lead to such ailments of the bone, with prolonged consumption. Skeletal fluorosis causes increased incidents of bone fracture, due to loss of elasticity of bones. Anion exchange of activated alumina is an effective treatment method for fluoride, along with reverse osmosis.


Above: a look at the flouridation equipment used inside a water treatment facility. Note the danger label at the left of the photo.

Barium, another naturally-occurring chemical, may be found in drinking water. It is safe to consume till the concentration of 0.7 mg/l .It has been observed to affect the renal system in laboratory tests, along with the potential to cause hypertension. Nitrite or nitrates may be released into water from contamination by effluents, as discharge from agricultural land, or contamination by oxidation of human/animal waste products. It could affect formula-fed infants between 3-6months of age, leading to methaemoglobinaemia in them. Methaemoglobinaemia, in conjunction with gastrointestinal disorders, in the presence of microbial contaminants in the water, could have a severe impact on infants, with immature immune systems. Chemicals, such as, Benzene, released in environment, from industrial and automobile emissions, may cause leukemia.

Risks associated with microbial and radiological contaminants in drinking water

Microbial quality of drinking water is a key determinant of human health. Microbial hazards account for infectious and fatal waterborne diseases. It is difficult to detect pathogenic microbes in drinking water, making it difficult to estimate their quantity/ potential effects and to combat them. Further, their potency varies, according to the intensity of invasion of various pathogens, exposing people with weaker/impaired immune system- such as the infants, the elderly and the chronically sick - to maximum damage. These pathogens proliferate in the host cells and in the water itself, with catastrophic effects on human health. The risk of waterborne diseases increases from intake of drinking water, contaminated with human/ animal excrement. However, some of the pathogens are naturally -occurring, found to thrive in water pipes, as well as the drinking water catchments. Greater awareness in the community and control measures for preventing the contamination of water by microbial pathogens may guard against the severity of waterborne diseases. Pathogenic viruses, including rotavirus or enterovirus can be transmitted through contaminated water and wreck havoc on human health, causing severe gastrointestinal infections in small children, meningitis, paralysis and critical cases of gastroenteritis. Disease-bearing bacteria, shigella, causes fatal waterborne epidemics in less-developed countries. Salmonella typhi leads to large-scale eruptions of typhoid. E.coli and vibrio cholerae are other examples of waterborne bacterial pathogens, producing high mortality rates. The waterborne pathogen campylobacter causes huge incidents of diarrhea, all over the world. Infectious gastrointestinal disorders are also caused by disease-bearing protozoa cryptosporidium and giardia, spread by fecal contamination. Contamination by naturally-occurring or man-made radionuclide also poses a serious threat to the safety of drinking water. Radiological contaminants that may be present in sources of drinking water are associated with risks of cancers. The WHO maintains an individual dose criterion regarding ingestion of radiological contaminants through drinking water, with no perceptible damage to human health.


The physical, chemical, microbial and radiological aspects of drinking water need to be plotted, monitored and controlled on a continuous basis , to ensure the supply and distribution of safe drinking water. Accessibility to safe drinking water can act as a protective shield against many pernicious diseases and lower the incidents of acute or chronic waterborne infectious diseases. Disinfectants, filtration, reverse osmosis and anion/cat ion exchange through activated metals, can be used to control chemical contaminants of drinking water. Control of microbial hazards, can be affected by single or multiple phases of treatments involving filtration, precipitation, sedimentation, coagulation, disinfection, effectively inactivating the microbial pathogens. Viruses and protozoa are resistant to filtration and disinfecting treatments, and generally require a rigorous control regime. In addition, approved methods of household treatment technologies including UV light, heat, filtration, and chemical disinfectants are used to inactivate microbes from drinking water. Also, proper storage and handling of drinking water by end-users is relevant to the quality/safety of drinking water. Local information about prevalence of contaminants or evidence of outbreaks of waterborne diseases is an invaluable resource for quality-control of drinking water, along with disease prevention. The role of community involvement and health regulators are vital for effective feedback regarding drinking water quality. Careful evaluation of health-related risks associated with drinking water, needs to be conducted by national authorities. Consequently, plans for ensuring safety of drinking water through regular mapping, monitoring, reviewing, documenting and verifying the source-supply-distribution of drinking water, in line with WHO recommendations, can go a long way in preventing waterborne diseases and protecting human health.


1. The WHO guidelines on drinking water quality : http://www.who.int/water_sanitation_health/dwq/gdwq0506.pdf

2. Enhancing drinking water quality: periodic reviews and implementation of the WHO guidelines : http://www.health.gov.bc.ca/public-health/pdf/Water_Quality_Drinking_Water-Evidence_Review.pdf

3. Risk assessment based on physical and chemical quality of drinking water: http://www.ipublishing.co.in/ijesarticles/twelve/articles/volthree/EIJES31120.pdf http://water.epa.gov/drink/contaminants/#Radionuclides

4. Risks associated with microbial and radiological contaminants in drinking water : http://www.glerl.noaa.gov/seagrant/ClimateChangeWhiteboard/Resources/Mac2/waterborne%20pathogens.pdf

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