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1 Mar
Water Quality
By WAE Corp on "Water Quality"

Is your water safe to drink? – Guidelines by World Health Organization

“Pure water is the world’s first and foremost medicine”. The same water if contaminated is the leading cause of diseases and deaths around the world! This article summarizes the guidelines for drinking water quality mentioned by the World Health Organization. Have a read before taking another gulp.

Full Article

What is in the water we drink? Why sometimes drinking water makes us sick? Why the water if contaminated, causes fatal diseases like viral hepatitis, cholera, typhoid, dysentery etc.?

Even today, the ‘so-called’ development all around the planet could not leave the ill-fated water-borne diseases behind! Not only that, contaminated water is the leading cause of diseases and deaths around the world with 3.4 million people dying of waterborne diseases every year, as per WHO. In India alone, the Central Bureau of Health Intelligence and ministry of health reported that from 2014 to 2017, one died every 4 hours due to contaminated water.

The above facts unravel the implications associated with contaminated drinking water and shout for themselves as to why determining the quality of water is so important. Therefore, we ought to know the major contaminants in water and be careful of the quality of water we drink.

Following are the major classifications listed to analyze the drinking water quality before the water is safe to drink.

Chemical Analysis

Total Dissolved Solids

TDS in water supplies originate from natural sources, sewage, agricultural run-off and industrial wastewater. The filterable residue after evaporation and drying of a water sample corresponds to the Total Dissolved Solids.

The TDS in the water sources is commonly tested by the measurement of specific conductivity with a conductivity probe that detects the presence of ions in water. Conductivity measurements are converted into TDS values by means of a factor that varies with the type of water.

The presence of TDS in water may affect the palatability but no recent data on health effects associated with the ingestion of TDS in drinking water appear to exist. Therefore, no health-based guideline value is proposed for TDS; however, drinking water guidelines are available for some of its constituents like boron, fluoride and nitrate.

Biological Oxygen Demand

It is an approximate measure of the amount of biochemically degradable organic matter in a water sample produced by micro-organisms through biochemical oxidation of that organic matter with the help of atmospheric oxygen dissolved in the water.

5-day incubation period has been accepted as the standard for this test. As determined experimentally by incubation in the dark, BOD includes oxygen consumed by the respiration of algae.

No health-based guideline value is recommended. However, very high levels of dissolved oxygen may exacerbate corrosion of metal pipes.


Lead is present in tap water to some extent because of its dissolution from natural sources. But mainly, the presence of lead is from household plumbing systems in which the pipes, solder, fittings or service connections to homes contain lead. PVC pipes also contain lead compounds that can be leached from them and result in high lead concentrations in drinking water.

For testing the levels of lead in environmental and biological materials, atomic absorption spectrometry and anodic stripping voltammetry methods are used.

The guideline value is maintained at 10 µg/l but is designated as provisional based on treatment performance and analytical achievability.


It is a measure of a water source’s buffering capacity and exhibits the ability to neutralize acids. The total alkalinity is identical with its bicarbonate alkalinity and is reported in mg/l as CaCO3. The alkalinity of some water sources is due to the presence of the bicarbonates of calcium and magnesium, the pH of which does not exceed 8.3.

The test of Alkalinity is done by titration of the same water with a standard solution of a strong mineral acid. Electrometric titration method is performed in order to determine high levels of accuracy while testing the level of Alkalinity.


Acids and Alkalis are normally extremely dilute in the drinking water. Although pH alone is not the primary determinant of health impact on water consumers yet it is one of the most important operational water quality parameters. In order to ensure satisfactory water clarification and disinfection, careful attention to pH control is necessary at all stages of water treatment.

The pH of an aqueous sample is usually tested electrometrically with a glass electrode. Temperature has a significant effect on pH measurement.

No health-based guideline is proposed for pH.


High concentration of chloride gives a salty taste to water and beverages.  The salty taste depends on the ions with which the chlorides are associated like sodium, calcium and magnesium. High chloride content may also indicate pollution by sewage or industrial wastes or by the intrusion of seawater or saline water into a freshwater body or aquifer.

The test for chloride concentration in the water sample is done by titration with standard silver nitrate or Mercuric Nitrate method can also be used.

Chloride concentrations in excess of about 250mg/l can give rise to detectable taste in water but otherwise, no harmful effects of prolonged intake of chloride have been observed in the humans. No health-based guideline value is proposed for chloride in drinking water.


Chlorine is used as disinfectant and bleach for both domestic and industrial purposes and is widely used to disinfect drinking water.

In order to test free chlorine concentrations in water, a colorimetric method can be used at concentrations of 0.1-10 mg/litre.

The guideline value is 5 mg/l. Most individuals are able to taste chlorine or its by-products at concentrations below 5 mg/l and some at levels as low as 0.3 mg/l.


Fluoride is one of the major ions in seawater and is therefore indicative of most natural water concentrations. It may also be added to drinking water to assist in the control of dental caries.

The tests to check fluoride concentration are selective ion electrode method, SPADNA colorimetric method or Fluoride distillation method.

The guideline value is 1.5 mg/l. Values higher than that carry an increased risk of dental fluorosis and the progressively higher concentrations lead to increased risks of skeletal fluorosis.


When directly pumped from the well, anaerobic groundwater may contain ferrous iron at concentrations up to several milligrams per litre without discolouration or turbidity in the water. When exposed, the ferrous iron oxidizes to ferric iron, giving an objectionable reddish-brown colour to the water. Iron also promotes the growth of ‘iron bacteria’ which deposit a slimy coating on the piping.

Iron concentration can be determined by atomic absorption spectrometry or by colorimetric methods.

Although turbidity and colour may develop, there is usually no noticeable taste at iron concentrations below 0.3 mg/l. Iron concentrations of 1-3 mg/l can be acceptable for people drinking anaerobic well-water. No health-based guideline value for iron has been proposed.


When nitrogenous organic matter is destroyed by the microbiological activity, ammonia is produced and is therefore found in many surface and groundwater. Natural levels of ammonia in groundwater are usually below 0.2 mg per litre. However, ammonia does react with chlorine to reduce free chlorine and form chloramines.

The test for ammonia can be done through distillation under alkaline conditions followed by titration with standard acid.

The threshold odour concentration of ammonia at alkaline pH is approximately 1.5 mg/l and a taste threshold of 35/l has been proposed for the ammonium cation. No health-based guideline value has been proposed by WHO as it is not of direct relevance to health in the concentrations to be expected in drinking water.


In treated water, for drinking purposes, naturally occurring aluminium, as well as aluminium salts used in the alum coagulation process, are the primary sources of aluminium in drinking water.

To test the aluminium concentration, it is reacted with pyrocatechol violet followed by spectrometric measurement of the resulting coloured complex. 

Available evidence does not support the derivation of a health-based guideline value in drinking water even though aluminium concentrations in excess of 0.1-0.2 mg/l often leads to deposition of aluminium hydroxide floc and the exacerbation of discolouration of water by iron. In general, no long-lasting effects on health could be attributed to the known exposures from aluminium in the drinking water (Clayton, 1989).  Aluminium evidently has beneficial effects as a coagulant in the water treatment process and a number of approaches are available for minimizing residual aluminium concentrations in the same.

Microbiological Analysis

Bacterial Pathogens

The presence of Thermotolerant (faecal) coliforms nearly always indicates faecal contamination. Usually, more than 95% of the thermotolerant coliforms isolated from water are the gut organism Escherichia coli, the presence of which is proof of faecal contamination. Therefore, it is often unnecessary to undertake further testing to confirm the specific presence of E.coli.

The test can be done through Multiple Fermentation Technique and Membrane Filter Technique.

The concept of using organisms like E. coli as indicators of faecal pollution is a well-established practice in the assessment of the quality of drinking water. Furthermore, heterotrophic bacteria can be used as operational indicators of disinfection effectiveness and distribution system cleanliness. Clostridium perfringens and coliphage can be used to validate the effectiveness of treatment systems.

Viral Pathogens

Viruses in drinking water can cause acute diseases and a wide variety of infections involving different ways of transmissions, routes and sites of infection and routes of excretion. Viruses like Adenovirus, Enterovirus, Hepatitis A, Hepatitis E, Rotavirus, Norovirus and Sapovirus can significantly affect human health, gastroenteritis being the most common condition (often called stomach flu) as viruses associated with waterborne transmission predominantly infect gastrointestinal tract and are excreted in the faeces of infected humans.

Protozoan pathogens

Protozoa and Helminths are among the most common causes of infection and disease in human and animals. Most of the pathogens produce cysts, oocysts or eggs that are extremely resistant to processes commonly used for the disinfection of water and in some cases can be difficult to remove by filtration processes, therefore, controlling their waterborne transmission present real challenges.

The protozoans that have high health significance are Acanthamoeba, Cryptosporidium parvum, Cyclospora cayetanensis, Entamoeba histolytica, Giardia intestinalis, Naegleria fowleri and Toxoplasma gondii. They have high resistance to chlorine and therefore high relative infectivity among humans. Some of these organisms cause ‘emerging diseases’, Cryptosporidiosis being the most notable of them caused by a protozoan pathogen.

Helminth pathogens

Helminth refers to all types of worms, both free-living and parasitic. Helminth parasites infect a large number of people and animals worldwide. Apart from the two exceptions - Dracunculus medinensis and Fasciola spp., drinking water is not a significant route of transmission for most helminths. Their exposure can cause acute and chronic infections among humans.

Once it is established that biological methods will provide useful information in a monitoring programme, an appropriate technique must be selected from the five categories of the principal biological methods which are Ecological Methods, Physiological and biochemical methods, Controlled biotests, Contaminants in biological tissues and Histological and Morphological methods.

Physical Analysis


Suspended particles or colloidal matter obstruct the light transmission through the water which causes Turbidity in the water. Turbidity causes visible cloudiness in the water which might have a negative impact on the consumer acceptability of water. Although turbidity may not necessarily be a threat to health yet it is an important indicator of the possible presence of contaminants that would be of concern to health.

 Turbidity is measured by nephelometric turbidity units (NTU) and can be initially noticed by the naked eye above approximately 4 NTU.

To ensure the effectiveness of disinfection, turbidity should be no more than 1 NTU and preferably much lower.

Taste, odour and appearance

Aesthetic acceptability is the first determinant for a common man to decide the quality of water. Taste, odour and appearance can originate from natural inorganic and organic contaminants, biological sources, synthetic chemicals, corrosion and problems in the water treatment process. Taste and odour in drinking water may indicate some form of pollution or malfunction during water treatment and distribution. These aesthetic problems can be prevented through conventional treatment processes such as coagulation, sedimentation and chlorination and specific treatments like aeration, granular or powdered activated carbon and ozonation.

The above mentioned drinking water quality guidelines by World Health Organization provide thorough guidelines, international reference points and recommendations on water quality and human health, encompassing a lot more parameters to analyze and test the quality of drinking water. These guidelines form the basis for regulation and standards setting worldwide.

“Pure water is the world’s first and foremost medicine”. The quality of water can make or mar your health. Think before you gulp!  



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