Water analysis - General Methods

    Water-borne diseases are caused by many pathogenic bacteria, viruses, protozoa etc. Among the bacterial infections that are spread by water are cholera, enteric fevers, dysentery. Among the viruses, Hepatitis A, poliovirus cause infections after drinking contaminated water. Among the protozoa Amoebic dysentery caused by the protozoan Entamoeba histolytica and those caused by Giardia lamblia, Balantidium coli and Cryptosporidium species which is spread either by drinking contaminated water or by eating food such as fresh fruit, salad or raw vegetables that have been washed in contaminated water. Among the helminthes are Schistosomiasis caused by worms of the genus Schistosoma.

Since it is impossible to test for every pathogenic microorganism, we test for the presence of indicators to decide the potability of drinking water. 

WHO standards say that 

1) potable (drinking) water should have no fecal coliform per 100 ml 

2) potable (drinking) water should have no more than 4 coliforms per 100 ml. 

If more than these are observed, appropriate treatment method should be undertaken.

General Rules of Sampling

1) Wash your hands thoroughly before and after collecting samples.

2) Collect microbiological samples in sterile bottles.

3) Take care to avoid contaminating the sample container and water sample.

4) Label the bottle before sampling.

5) Take a minimum of three samples of each and from different areas of water body.      

6) Perform the analysis immediately and if any delay is there, store the samples at 4 degree C. 

Water Analysis

In short, the different methods of water analysis are

(1) General Methods

1. Total Count/ Heterotrophic Plate Count (HPC)/Colony  Count/Plate count

2. Membrane Filter Method

(2) Specific Methods

1. Coliforms

1. MPN 

2. Colilert defined substrate test 

3. Differential Coliform Test

4. IMViC 

2. Fecal Streptococci  

1. Azide-dextrose/ Glucose azide broth

3. Clostridium perfringens      

1. Litmus Milk Test

4. Pathogenic bacteria  

Specific Methods, if need arises

 

General Methods:

1. Total Count/Heterotrophic Plate Count/Colony Count/SPC-Simple/Standard Plate Count

Small volume of diluted sample pipetted on to surface of the medium and pour plate performed. Incubation at 20-22^oC for 3 days (saprophytes) and/or 37^oC for 24 h (potential pathogens). Count the plate with dilutions which give between 30 - 300 colonies.

Used for general purposes like: 

 Idea about heterotrophic bacterial content of water

 Test the efficiency of water treatment processes

(Pour plate - 1 ml of appropriately diluted inoculum is added to 15 ml of molten agar and poured on petridish. After incubation, Colonies appear throughout the depth of medium. Used to estimate viable count.)

 

                                                                        

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