Water quality field testing conventionally depends on membrane filtration, but due to the cost and complexity of the equipment involved, this article presents alternative methods.

Key field tests

• Membrane Filtration
• Presence/Absence
• Petrifilm

A water quality field test should be simple, rapid, inexpensive, and accurate. These tests estimate the amount of fecal Coliform present in the water. Fecal Coliform is not a pathogen. It is used as an indicator of pathogen presence because Coliform bacteria are very common in the feces of warm blooded animals and their presence is relatively easy to test for. Coliform are acceptable in water sources so long as their concentration is relatively low.

Table 1 shows fecal Coliform ranges and the actions which should be taken depending on the Coliform count

Recommended approach

• 3 10ml samples should be taken from every potential water source and a P/A test conducted.
• If these samples are all negative, the water source is usable.
• If there are positive results from the P/A test, a Petrifilm test should be conducted
• Since the petrifilm range is limited to above 100cfu/100ml, it is possible to get negative results from this step. If this is the case, the water is not deemed safe, but must be tested with 10 10ml P/A samples to assess the MPN.

Conclusion

The major advantages of Petrifilm and P/A over standard Membrane filtration are that they are easier to use and can be incubated at lower temperatures. It is recommended that the samples be kept in a pouch such as a money belt for the 24 hours. Experience shows that the human body temperature of 37 Celsius is adequate for performing these procedures.

Credits

This material is originally adapted from content found here but this work is entirely original and released under GNU FDL.

References

Médecins Sans Frontières (1994) Public Health Engineering in Emergency Situation. Médecins Sans Frontières: Paris.