Water Sampling

Sampling Of Bacteria From Water

Direct microscopic examination of water sample generally reveals few bacteria. The filtration technique is used to isolate the bacteria for their estimation per unit volume, as well as to study them morphologically. The membrane filters provide a rapid and useful means of sampling from water. Such filters are also used for viable counting by laying on a suitable agar plate and allowing to form colonies. The filtration procedure for direct counting is given below:


  • Water sample
  • Membrane filter assembly
  • Millipore filter (0.45 µm)
  • Side arm flask
  • Suction pump
  • Nutrient agar plates (pH 6.8)


  1. Place a millipore filter in the membrane filter assembly and connect it with flask.
  2. Connect the other side of the flask with suction pump.
  3. Allow the water sample to filter through millipore filter paper.
  4. Take out the filter paper and transfer on the surface of nutrient agar medium in Petri plates.
  5. Incubate the plates at 28 C for 24 hours and observe the growth of bacterial colonies.


The number of colonies can be calculated by counting in terms of CFUs/ml of sample.


Dr. R. C. Dubey – Practical Microbiology

Gaurav Singh

Editor in Chief Medical Microbiology & RDT Labs - RDT Labs Magazine | BSc Medical Microbiology | MSc Microbiology

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