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Microbiological Testing of Water

It has been appositely said, “Pure Water is the World’s First and Foremost Medicine.” But do you know that the water you consume and use in formulation of products could be contaminated with disease causing microorganisms – pathogens? 

Whether you have pharma business, cosmetic business, food or beverage business or you need water testing reports for any regulatory requirement, it is indispensable to get your water sample tested from an authorised laboratory. Certainly, your business needs a periodic microbiological analysis of water to fulfil regulatory requirements and to gain immense trust of consumers in order to flourish in the market.

The World Health Organisation estimates that 1.1 billion people have water sources contaminated with faecal microorganism. Pathogenic microorganism enters the water due to poor water quality control and sanitation practices.

Interestingly, Microbiological analysis is the most effective way to detect faecal contamination in water. Obtrusively, faeces of humans, animals, birds and livestock enters the water and makes it unfit for consumption. Microbiological analysis of water is an important aspect of water testing.

Water microbiology is related to the microorganisms that live in water and it can be easily transported from one habitat to another by water. 

Ironically, water can sustain the growth of different kinds of microorganisms which can prove to be beneficial for all of us however on the contrary growth of several bacteria in contaminated water can make it injurious for our health and environment. 

Primarily, the bacteria found in intestinal tracts of humans and warm-blooded animals like Escherichia coli, Salmonella, vibrio and Shigella can enter the water through faeces thereby making the water fatal for consumption. Moreover, the intestinal tracts of warm-blooded animals carry viruses like rotavirus; enterovirus etc. which contaminates water and makes it inapt for use.

What is microbiological testing of water?

It is significant to understand the microbial quality of water this is why testing of drinking water to ensure that it is safe must be a priority to avoid any deleterious consequence.

The microbiological testing is performed while using faecal indicator bacteria prominently Escherichia coli as these bacteria indicate the presence of faecal contamination rather than identifying the pathogens directly. This analysis is performed in the laboratory using proper procedures to get consistent results.

Further, the presence of soil in water indicates microorganisms which could be detected through turbidity of water. The presence of bacteria and viruses could decrease the clarity of the water.

Turbidity is a quick way to detect whether the water quality is deteriorating or not. To set the seal on Good manufacturing practices it is quite intrinsic to evaluate microbial content and chemical purity of water samples.

How do you test for microorganisms in water?

Microbiological water testing is the appropriate way to check for microorganisms in water. To steer clear of any risk and ensure prevention from disease it is essential to get microbiological testing of drinking water supplies routinely as per the international standards.

Coliform and indicator organisms

One of the best standards for easy isolation, detection and enumeration for microbial water testing is Coliform (a group of gram-negative bacteria that can ferment lactose with a production of gas within 48 hours at either 35ºC or 44/44.5ºC.) When enteric pathogens or viruses are detected in water testing, coliform is always present in it. However, a high ‘total coliform’ count would always require further analysis to confirm faecal coliforms. Escherichia, Enterobacter, Klebsiella are the faecal coliforms, and Citrobacter and Serratia are specifically found in plants and soil. The presence of faecal streptococci/Enterococci confirms faecal contamination.

Rapid Methods

The IDEXX Colilert uses a colorimetric ONPG assay to detect coliforms and a fluorescence MUG assay for E. coli. Colilert can simultaneously detect these bacteria within 18-24 hours, depending on the product. It can also suppress 2 million heterotrophic bacteria per 100 mL present. The Enterolert Test from IDEXX uses a proprietary Defined Substrate Technology (DST) nutrient indicator to detect enterococci.

Membrane filtration

Membrane Filtration method requires quite a trifle incubator space and it can lucidly handle large volumes of water too. It is one of the most preferred methods to detect indicator organisms for microbiological testing of water. In this method specific volume of water is passed through a sterile membrane filter with small pore size in order to retain bacterial cells. The filter is then transferred aseptically to the surface of an agar plate, or an absorbent pad saturated with a suitable selective medium and incubated. Colonies are allowed to develop on the surface of the filter to examine directly.

Culture media

Recommended media for coliforms and E. coli include membrane lauryl sulphate broth or agar. Membrane enterococcus agar (mEA) and membrane-Enterococcus Indoxyl-ß-D-Glucoside Agar (mEI) can be used for detection and enumeration of enterococci, while Tryptose sulphite cycloserine agar without egg yolk can be used to culture Clostridium perfringens on membrane filters. 

Further culturing or biochemical testing can then be used to confirm the identity of suspect colonies growing on filters placed on selective media. Apparently, chromogenic and fluorogenic media are used in water microbiology.

Traditional culture

The traditional culture method is still used for enumerating heterotrophic bacteria however this technique of using pour and spread plate count methods has its own limitations, consequently ‘most probable number’ (MPN) technique came in fore.

In this method measured volumes of water sample are added to a series of tubes containing differential. Growth is indicated by a colour change in the medium, and the result is calculated from the distribution of positive tubes. Due to certain limitations and drawbacks this method is only useful for occasional tests conducted in small laboratories and commercial test kits based on MPN methods are available for coliforms and enterococci.

Legionella in cooling towers

Legionella pneumophila, is an organism that has a higher tolerance for chlorine moreover it can live within the cells of parasites. Cooling towers provide suitable conditions for L. pnuemophila and unfortunately provide a perfect transport for its dissemination via droplets into the atmosphere and leads to severe disease.

Water quality parameter

Nitrogen (NO3-N)

Nitrogen is vital for growth of plants in an aquatic ecosystem and it occurs naturally in both fresh and saltwater. When nitrogen exceeds and comes into the stream ecosystem. It leads to excessive algal growth which ultimately depletes the available oxygen. This becomes deplorable for aquatic life.

Total Coliform

Total coliform bacteria, faecal coliform bacteria, and E. coli are all indicators of water contaminated with faecal matter. Contaminated water may contain other pathogens which are more difficult to test for. Therefore, these indicator bacteria are useful in giving us a measure of contamination levels.


The faecal matter of humans, animals, birds and mammals carry a bacterial species known as E. coli.  Total coliform bacteria are an entire group of bacteria species including E. coli species.

There are certain forms of coliform bacteria that do not live-in faecal matter but instead live-in soils. Notably, most of the faecal coliform cells found in faecal matter are E. coli. This is why, all E. coli belong to the faecal coliform group, and all faecal coliform belong to the total coliform group.

What is the microbial limit for drinking water?

Food businesses are primarily required to submit a water testing report of the water they are using in their processes, confirming its compliance to the potable water standard (IS 10500:2012) prescribed by the Bureau of Indian Standards.

They are required to either submit a complete report or a report covering the essential parameters including physical, chemical and microbiological parameters.

Significantly, the water testing report must be obtained from an FSSAI recognized and NABL accredited laboratory. Besides, it is essential that the sampling is carried out by the laboratory and the report must contain the details of the date of sampling and the person carrying out the sampling.

Microbial limits

  • Escherichia coli shall be absent in any 250 ml sample when tested in accordance with the method given in IS 5887 or IS 15185.
  • Coliform bacteria shall be absent in any 250 ml sample when tested in accordance with the method given in IS 5401 or IS 15185.  
  • Faecal streptococci and Staphylococcus aureus, shall be absent in any 250 ml sample when tested in accordance with the method given in IS 5887. 
  •  Streptococci (Enterococci) may also be tested by the method specified in IS 15186.
  •   Aerobic Microbial Count The total viable colony count shall not exceed 100per ml at 20to 22°C in 72h on agar-agar or on agar-gelatine mixture, and 20 per ml at 37°C in 24 h on agar-agar when tested in accordance with the methods given in IS 5402.
  •    Salmonella and Shigella, shall be absent in any 250 ml sample when tested in accordance with the method given in IS 5887. 

Our labs for microbiological testing of water

Albeit microbial limits could be low and harmless however several microbiological studies manifest that the quality of bottled water for sale did not meet regulatory standards and guidelines. Due to the presence of pathogens in low numbers, it becomes difficult to monitor, this is why it is significant to check for indicator microorganism.

We carry out sampling and analysis of water samples from hotels, restaurants, canteens, food processing units, manufacturing units, factories, retail outlets and all other food businesses.  

Our laboratories are accredited by the National accreditation board for testing and calibration laboratories (NABL) and also recognized by the Food Safety and Standards Authority of India (FSSAI).We have our presence in  New Delhi, Himachal Pradesh, Haryana, Bangalore and Karnataka with an aim to support our clients across India and around the world. 

Contact us to get your water tested in our state-of-the-art modern microbiology laboratory. Our personnel will visit you to collect the samples in required temperature for microbiological testing of water. 


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