Drinking Water Quality Standard

Drinking Water Quality Standards (WHO Guidelines)

Drinking water quality standards gives the important quality parameters set for drinking water.

These drinking water quality standards describe the allowable limit and permissible limit in the absence of an alternate source. It is recommended that the allowable limit should be applied because water exceeding those values mentioned under ‘Acceptable’ is not appropriate.

However, such a value can be tolerated in the absence of an alternative source. However, if the value exceeds the limit indicated under the permissible limit in the absence of an alternative source, the sources have to be rejected.

Pesticide residue limits and test methods included in the document are based on consumption patterns, persistence, and available manufacturing data.

Wherever available, limits are specified based on WHO guidelines. In cases where WHO guidelines are not available, the standards available from other countries have been examined and incorporated keeping in view the Indian circumstances.

This amendment includes additional requirements for ammonia, chloramine, barium, molybdenum, silver, sulphide, nickel, polychlorinated biphenyls, and trihalomethanes, while color, turbidity, total hardness, free residual chlorine, iron, magnesium, mineral oil requirements Have been included. Boron, cadmium, total arsenic, lead, polynuclear metric hydrocarbons, pesticides, and bacterial requirements have been revised.

Read More: Water Treatment Process Steps

What is Drinking Water:

glass of water - Drinking Water Quality Standards
Drinking Water

Drinking Water is water to drink and for human consumption cooking purposes from any source. It also includes water (Treated or untreated) supplied to humans in any way the consumption. Drinking water which  is also called as  potable water, is water that is safe to drink or use for food preparation.

Range of Drinking Water Quality Standards:

Although drinking water standards India is often referred to as simple lists of parametric values, the standards documentation also specifies sampling location, sampling methods, sampling frequency, analytical methods, and laboratory validation AQC.

In addition, many standards document also require calculations to determine if the level exceeds the standard, such as taking an average. Some benchmarks provide complex, detailed requirements for statistical treatment of results, temporal and seasonal variations, the sum of related parameters, and apparently mathematical treatment of the results.

Drinking Water Standards India

Basic Drinking Water Quality Standard Parameters (WHO Guidelines):

Following are some important drinking water quality standards in India.

  1. Turbidity
  2. Colour
  3. pH
  4. Taste and odour
  5. Hardness
  6. Total Suspended Solids (TSS)
  7. Total Dissolved Solids (TDS)
  8. Alkalinity
  9. Chlorine
  10. Nitrate
  11. Sulphate 
  12. Fluoride
  13. Zinc 

1. Turbidity:

Turbidity is caused by suspended material that absorbs and disperses light. These Colloidal and finely dispersed turbidity-causing materials are not arranged under quiescent It is difficult to overcome by circumstances and sedimentation.

Turbidity is a major parameter in Water supply engineering, because both turbidity will lead to water beauty Unpleasant and causal problems in water treatment processes, such as filtration and Disinfection.

Turbidity is also used to indicate evidence of the possibility of Bacteria is present. Turbidity measurements made using proprietary nephelometric devices are Expressed as Nephelometric Turbidity Units (NTU).

2. Colour:

There are many surface water colours, mainly due to the decomposition of organisms, metallic Salts, or coloured clay. This colour is considered as a “clear colour” because it is seen inside. The presence of a suspended substance, while the “true colour” is obtained only by dissolution Inorganic and Organic Matters.

Samples can be centrifuged and/or filtered Turbidity to accurately measure colour. Water that derives its colour from natural organic matter usually does not create any health risk. However, due to the yellow-brown appearance of such water, Water may not be aesthetically acceptable to consumers.

Consumers of excessive Colourful but already properly treated water cannot be believed that the water is actually cured Taken treatment. Many processing industries require less coloured water. The pub needs a drink Water to meet “highest desirable” World Health Organization (WHO) standards Less than 5 colour units.

A standard colour unit is defined as a 1 mg / L concentration of platinum Potassium chlorophane. Colour measurement is compared by Sample with a standard colour solution using a spectrophotometer. a straight line of the calibration curve is initially developed by plotting platinum-cobalt versus absorber Colour standard.

In practice, the absorption of a sample is determined and While measuring the true colour, pre-treatment has to be done to remove turbidity.  There is effect of  centrifugation or filtration on the true colour. so, when Specify the correct colour value reporting, pre-treatment method and its description operating conditions.

Similarly, the colour value of water is highly dependent on pH, and as the pH of water is raised, always increases. When reporting a colour value, Specify the pH at which the colour is determined.

Drinking Water Quality Standards

3. pH Value:

PH Value indicates the hydrogen-ion concentration of a solution. In the form of acids and the bases in the solution dissociate to produce hydrogen ions [H +] And hydroxyl ions [OH-] Respectively, pH is used to indicate the intensity of an acidic or alkaline state. Remedy.

Alkalinity is the measure of acid-neutralizing capacity in dissolving substances. Is equal to the amount of strong acid required to dilute the solution from water and initial pH at around 4.5. Many materials can contribute to the alkalinity of water.

This is mainly due to the presence of salts of weak acids (mainly bicarbonate and) Carbonate) and hydroxide (at high pH). PH and alkalinity are important water quality parameters in environmental engineering Do the exercises.

In the area of water supply and treatment, these parameters are very good Effects on chemical coagulation, disinfection and softening processes, and Corrosion Control for Water Distribution Pipe Networks. of effective chemical coagulation for example, water is only within a specific pH range.

Chemicals used for Coagulation release, as a by-product of their reactions with water to make it insoluble. Hydroxide precipitated, hydrogen ion (acid-factor). When uncontrolled, this hydrogen Ions can lower the pH of water so that coagulants are rendered ineffective.

The presence of sufficient amount of alkalinity in water can react and remove Hydrogen ions released by coagulants, thus buffering water in the pH range Where coagulant can be effective. In pure water, the water molecules separate into equal amounts of hydrogen and hydroxyl. Ions (10–7 moles / L). From the law of mass action, it can be shown that, for pure water About 25 ° C.

Read More: Environmental Impact Assessment(EIA) – Process & Importance

4.Taste and Odour:

If every water tap on the property has a taste or smell, it is likely the main water supply. If it occurs only in a few taps, the problem is of the fixtures or pipes that supply those specifics. tap.

If after a few minutes of running water, the problem goes away, then the problem is somewhere in your home plumbing system.

The best way to reduce the taste and smell caused by your plumbing is to run the tap for several minutes, pour a little water in a container, and then store it in the refrigerator. You can also consider installing a certified water filter.

Petroleum, gasoline, turpentine, fuel, or solvent odours: These odours are rare but potentially severe. Do not use water. A leaking underground storage tank can contaminate your water supply.

Metal flavour:

Iron or copper can leach from the pipe into the a water. Less common metals, such as Zinc and manganese can also be a problem. If you are worried, have your water analysed Contact a certified laboratory, or your water utility.

Chlorine, chemical, or medicinal taste or smell:

Adding or interacting with chlorine in water the formation of organic materials in your plumbing system may cause chlorine taste or odour Strong. It is not usually an immediate health hazard. If you find the taste or smell strong, contact Water utility for your local health agency or advice.

Smell of Sulphur or Rotten Eggs:

Bacteria that grow in your sink drain or hot water heater may smell.  Naturally having hydrogen sulphide in your water supply can also cause this type of odour. To evaluate Reason, pour a small amount of water in a narrow glass, step away from the sink, turn the water around Inside the glass, and sniff it.

If there is no odour in the water, the potential problem is bacteria in the sink drain. If There is an odour in the water, it may be from your hot water heater. There is an element in your warm the water heater is designed to protect it from a corrosion.

Sometimes the element causes an odour of a sulphide It deteriorates over time. A authorized plumber may be able to evaluate this problem. If you get out of the drain and do not use the water heater and the smell is definitely coming from tap water.

Drinking Water Quality Standards

5. Hardness:

Hardness is defined as a measure of resistance to localized plastic deformation induced by mechanical indentation or friction.

In general, different materials differ in their hardness; For example, hard metals such as titanium and beryllium are harder than soft metals such as sodium and metal tin, or wood and common plastics.

Macroscopic stiffness is usually characterized by strong intermolecular bonds, but the behavior of solids under force is complex; Therefore, there are various measurements of hardness: scratch hardness, indentation hardness and rebound hardness. Hardness is dependent on flexibility, elastic stiffness, plasticity, stress, strength, toughness, viscosity, and viscosity.

Common examples of hard materials are ceramics, concrete, some metals, and super hard materials, which can be combined with soft materials.

6. Total Suspended solids (TSS):

Total Suspended Solids (TSS) is defined as a dry-weight of suspended particles that do not dissolve, in a sample of water that can be analyzed by a filter trapped by a filter.

It is a water quality parameter that is used to assess the quality of wastewater after treatment in any type of water or waterbody, for example, ocean water, or a wastewater treatment plant. It is listed as a traditional pollutant in the American Clean Water Act.

Total solute solid is another parameter acquired through a separate analysis that is also used to determine the quality of water, not dissolved suspended particles, based on completely dissolved substances within the water. Instead of TSS was previously called non-filterable residue (NFR), but was changed to TSS due to the ambiguity in other relevant topics.

Read More: Planning of Residential Building with 12 Principles of Building Planning

7. Total Dissolved solids (TDS):

Total Dissolved solids (TDS) are a measure of the dissolved combined content of all inorganic and organic materials present in a liquid in molecular, ionized, or micro-granular (colloidal sol) suspended form.

TDS concentrations are often reported in parts per million (ppm). TDS concentrations of water can be determined using a digital meter.

Generally, the operational definition is that solids must be sufficient to survive filtration through a filter with 2-micrometer (nominal size, or smaller) pores. Total solutes are generally discussed only for freshwater systems, as salinity includes ions with a definition of some TDS. The main application of Total dissolved solid is in the study of water quality for streams, rivers, and lakes.

Although Total dissolved solid is not generally considered a primary pollutant (as such it is not considered to be associated with health effects), it is used as an indication of the aesthetic characteristics of drinking water and the presence of a wider array of chemical contaminants. Is used as an aggregate indicator of.

The primary sources for Total dissolved solid in obtaining water are agricultural runoff and residential (urban) runoff, soil-rich mountain water, soil leaching contamination, and point source water pollution discharge from industrial or sewage treatment plants.

The most common chemical constituents are calcium, phosphate, nitrates, sodium, potassium, and chloride, which are found in nutrient runoff, normal storm water runoff and runoff from icy climates where road de-icing salts are applied.

Chemicals can be cations, ions, molecules or agglomerations on the order of a thousand or fewer molecules, so long as a soluble micro granule is formed. The more exotic and harmful elements of TDS are pesticides arising from surface runoff.

Some naturally dissolving solids originate from weathering and dissolution of rocks and soils. The United States has established a secondary water quality standard of 500 mg / l to provide drinking water volatility.

Drinking Water Quality Standards

8. Alkalinity:

Alkalinity refers to measuring the ability of water to neutralize acids. The alkalinity of water can be caused by the presence of one or more ions. These include hydroxide, carbonate, and bicarbonate. As discussed in previous articles, hydroxide ions are always present in water, even if the concentration is very low.

However, noticeable concentrations of hydroxide in the natural water supply are uncommon, but may be present after certain types of treatment. Small amounts of carbonate are found in the natural water supply in some parts of the country, rarely exceeding 3 or 4 grams (grains per gallon).

They can also be found in water after using lime soda to soften water. Bicarbonates are the most common source of alkalinity. The alkalinity of water can be defined as the ability to neutralize acids. Alkali substances in water include hydroxides or bases.

They can be detected by their pungent taste and by the fact that they turn red litmus paper into blue. Phosphates and silicates are rarely found in the home in a natural supply. These anion compounds can be used in various water treatment processes. These ions are certainly free in water, but have their counterparts in citations such as calcium, magnesium, and sodium or potassium.

Except for bicarbonate ions, when you are present in large quantities, you probably will not see an alkaline condition. Conversely, you should easily detect alkalinity due to the significantly lower amounts of carbonate and hydroxide ions. Strong alkaline water has an objectionable “soda” taste.

The EPA Secondary Drinking Water Regulations limit alkalinity to some extent by limits on total dissolved solids (500 ppm) and pH values.

9. Chlorine:

Chlorine levels of up to 4 mg per litter (mg / L or 4 parts per million (ppm)) in drinking water are considered safe. At this stage, harmful health effects are unlikely to occur. 

Microorganisms may be examined or found in raw water from rivers, lakes, and groundwater. While not all microorganisms are harmful to human health, there are some that can cause diseases in humans. These are called pathogens.

 The pathogens present in the water can be transmitted through a drinking water distribution system, causing waterborne diseases among its users. To combat waterborne diseases, various disinfection methods are used to inactivate pathogens.

With other drinking water treatment processes such as coagulation, sedimentation, and filtration, chlorination creates water that is safe for public consumption. Chlorination is one of several methods that can be used to disinfect water. This method was first used a century ago, and is still used today.

It is a chemical disinfection method that uses a variety of chlorine or chlorine-containing substances for oxidation and disinfection of a source of potable water.

Drinking Water Quality Standards


Chlorination can be done at any time / point during the water treatment process – there is not a specific time to add chlorine. Each point of the chlorine application will subsequently control a different water contaminant concern, thus offering a full spectrum of treatment from the time it leaves the water treatment facility to the time it leaves.

Pre-chlorination occurs when chlorine is applied to water immediately after entering the treatment facility. In the pre-chlorination step, chlorine is usually added directly to raw water (untreated water entering the treatment facility), or to a flash mixer (a mixing machine that ensures quick, uniform dispersion of chlorine is). Chlorine is added to raw water to eliminate algae and other forms of aquatic life from water, so that they do not cause problems in later stages of water treatment.

Pre-chlorination in the flash mixer is found to remove taste and odours, and regulate organic growth in the water treatment system, thus preventing growth in the sedimentation tank (where water is solidified by gravity) And filtration media (the filter through which the water passes after sitting in the sedimentation tank).

Oxidation of any iron, manganese, and / or hydrogen sulphide other than chlorine that are present will be removed, so that they can also be removed at the sedimentation and filtration stages. Filtration can only be done before filtration and also after sedimentation. It will control organic growth, remove iron and manganese, remove taste and odour, control algae growth and remove colour from water. This will not reduce the amount of biological growth in sedimentation cells.

Chlorination process almost can perform as a final step in the treatment process, which is when it is usually done in most treatment plants. The main purpose of this chlorine addition is to disinfect water and retain the chlorine residue that will remain in the water as it travels through the delivery system. Sometimes, chlorinating filtered water is more economical because a lower CT value is required. It is a combination of concentration (C) and contact time (T). The CT fact is discussed later on this fact sheet.

As long as the water has been through sedimentation and filtration, a lot of unwanted organisms have been removed, and as a result less chlorine and a shorter contact time are required to achieve the same effectiveness.

In order to support and maintain chlorine residual, a process, sometimes called re-chlorination, is carried out within the distribution system. This is done to ensure that proper chlorine residual levels are maintained throughout the distribution system.

10. Nitrate:

Nitrate is a compound that is formed naturally when nitrogen combines with oxygen or ozone. Nitrogen is one of the essential compounds for all living things, but high levels of nitrate in drinking water can be hazardous to health, especially for infants and pregnant women.

Nitrates are also made in large quantities by plants and animals and are released into smoke and industrial or automotive exhausts. Nitrate can occur naturally in the surface and groundwater at a level that is not usually the cause of health problems.

Sometimes, a high concentration of nitrate in well water often results in good construction, well location, and overuse of chemical fertilizers, or improper disposal of human and animal waste. Nitrate sources that may enter your well include fertilizers, septic systems, animal feedlots, industrial wastes, and food processing wastes.

After floods, wells can be more vulnerable to such contamination, especially if the wells are shallow, dug or bored, or submerged by floodwater for long periods of time.

Nitrate can be successfully extracted from water using treatment processes such as ion exchange, distillation, and reverse osmosis. Contact your local health department for recommended procedures. Warming or boiling your water will not remove nitrate.

Because some water will evaporate during the boiling process, the nitrate levels of water may actually increase slightly in concentration if the water is boiled. Mechanical filters or chemical disinfection, such as chlorination, do not remove nitrates from water.

11. Sulphate:

Sulphates are a combination of sulphur and oxygen and are part of the minerals found naturally in some soil and rock formations that include groundwater.

Sulphur generally helps in reducing bacteria, which use the sulphur as an energy source, are the primary producers of large amounts of hydrogen sulphide. These bacteria chemically convert natural sulphate into hydrogen sulphide by converting it into water.

Sulphur reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners, and water heaters. These bacteria usually thrive on the hot water edge of the water distribution system.

It is formed by the dissolution of underground deposits of organic matter such as decaying plant material. It is found in deep or shallow wells and can also enter surface water through springs, although it quickly escapes into the atmosphere. Hydrogen sulphide is often present in wells drilled in shale or sandstone, or near coal or peat deposits or oil fields.

Sometimes, a hot water heater is a source of hydrogen sulphide odour. The magnesium corrosion control rod is also found in many hot water heaters can chemically reduce sulphate to hydrogen sulphide.

Environmental Protection Agency (EPA) drinking water standards fall into two categories – primary standard and secondary standard. The primary standards are based on health considerations and are designed to protect people from three classes of toxic pollutants – pathogens, radioactive elements and toxic chemicals.

Secondary drinking water standards are based on taste, odour, colour, corrosiveness, foaming and staining properties of water. Sulphate is classified under Secondary Maximum Contamination Level (SMCL) standards. The SMCL for sulphate in drinking water is 250 mg per litter (mg / L), sometimes expressed as 250 per million (ppm).

Several methods of extracting sulphate from water are available. The chosen treatment method depends on a number of factors including the level of sulphate in the water, the amount of iron and manganese in the water, and if bacterial infection should also be treated. The choice you make also depends on how much water you have to treat.

Typical methods for treating small amounts of water (drinking and cooking only) may be distillation or reverse osmosis. The most common method of treating large amounts of water is ion exchange. This process works similar to a water softener. Ion-exchange resin, contained inside the unit, adsorbs sulphate. The resin should then be “regenerated” with a salt (sodium chloride) saline solution to allow further treatment.

The distillation boils the water to form steam which is then cooled and then the water is reassembled. Minerals, such as sulphate, do not evaporate with steam and are left behind in the boiling chamber. The reverse osmosis membrane has a pore that allows water molecules to pass through but leaves larger ions in solution.

12. Fluoride:

The Department of Health and Human Services (DHHS) sets the optimal level of fluoride for preventing tooth decay at 0.7 ppm, or 0.7 milligrams (mg) in every liter of water. The previously this numbers in force from 1962 to 2015, was 0.7 to 1.2 ppm. In 2015, it was revised to the lower limit.

Fluoridation of water is a controlled adjustment of fluoride to the public water supply to reduce tooth decay. Fluoride-containing water contains fluoride at a level that is effective at blocking cavities; This can occur naturally or by adding fluoride.

Mixed water works on tooth surfaces: in the mouth, it creates low levels of fluoride in saliva, reducing the rate of tooth enamel and increasing the rate at which it remineralizers in the early stages.

A fluoridated compound with cavities is usually added to drinking water, a process that costs an average of $ 1.11 per person in the US. When the naturally occurring fluoride, level exceeds the recommended limit.

Drinking Water Quality Standards

13. Zinc:

Zinc is naturally present in water. The average zinc concentration in seawater is 0.6–5 ppb. Rivers typically contain between 5 and 10 ppb zinc. Algae contain 20–700 ppm, marine fish and shells have 3–25 ppm, oysters have 100–900 ppm and shrimp fish have 7–50 ppm.

The most important zinc ores include sphalerite (ZnS) and smithsonite (ZnCO3). These compounds end up in water at the places where zinc ores are found.

About three-quarters of the total zinc supply is used in metal form. The remainder is applied in various industries as various zinc compounds. Industrial wastes that contain zinc stem from galvanic industries, battery production, etc. Zinc compounds are applied for many different purposes.

Zinc chloride is applied for parchment production, zinc oxide is a component of salts, paints and catalysts, zinc vitriol is applied as a fertilizer, and zinc bacitracin is applied as a growth stimulant in animal husbandry is.

The bulk of zinc in wastewater is not from point sources. It stems from large surface waters containing the element. Zinc leaks from zinc pipes and rain pipes, resulting in the circulation of carbon-rich water. Car tires with zinc and motor oil from zinc tanks release zinc compounds on the roads. Zinc compounds contain fungicides and pesticides, and consequently end up in water.

When insufficient safety measures are taken, zinc can be extracted from chemical waste dumps and landfills, or from dredge mortars.

Drinking Water Quality Standards Table:

Following are drinking water standards considered in India.

Sr. No: Parameter Desirable Limit Remarks
1. Colour (Hazen units, max.) 5 It may be extended up to 50 if toxic substances are suspected
2. Turbidity (NTU)   10 It may be relaxed up to 25 in the absence of alternate
3. pH 6.5 to 8.5 It may be relaxed up to 9.2 in the absence
4. Total Hardness (as CaCO3), mg/l, max.) 300 It may be extended up to 600
5. Calcium as Ca (mg/l) 75 It may be extended up to 200
6. Magnesium as (mg/l) 30 It may be extended up to 100
7. Copper as Cu (mg/l) 0.05 It may be relaxed up to 1.5
8. Iron (mg/l) 0.3 It may be extended up to 1
9. Manganese (mg/l) 0.1 It may be extended up to 0.5
10. Chlorides (mg/l) 250 It may be extended up to 1000
11. Sulphates (mg/l) 150 It may be extended up to 400
12. Nitrates (mg/l) 45 No relaxation
13. Fluoride (mg/l) 0.6 to 1.2 If the limit is below 0.6 water should be rejected, Max. The limit is extended to 1.5
14. Phenols (mg/l) 0.001 It may be relaxed up to 0.002
15. Mercury (mg/l) 0.001 No relaxation
16. Cadmium (mg/l) 0.01 No relaxation
17. Selenium (mg/l) 0.01 No relaxation
18. Arsenic (mg/l) 0.05 No relaxation
19. Cyanide (mg/l) 0.05 No relaxation
20. Lead (mg/l) 0.1 No relaxation
21. Zinc (mg/l) 5.0 It may be extended up to 10.0
22. Chromium as Cr+6 (mg/l) 0.05 No relaxation
23. Mineral Oil (mg/l) 0.01 It may be relaxed up to 0.03
24. Residual free Chlorine (mg/l) 0.2 Applicable only when the water is chlorinated

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