Water Testing

There is no need to test for specific pathogens (for each disease). Not only would that be slow and very expensive, but it would actually tell us less than we need to know. What we really want to know is, not only whether the water could make someone sick at present, but whether it is inclined to. In other words, if we did test for a specific disease, and found it was not there, shortly thereafter, if the disease appeared in the community, our test result would not have told us whether the water point could become a point of transfer.

What WatSan workers actually test for (what they use as an indicator) is coliforms. Because they are the indicator of choice, quick and inexpensive tests have been developed for them. When there are coliforms in the water, we know the water is subject to contamination, and that when disease does occur in the population, the water will carry, along with the usual coliforms, the pathogens being expelled by the sick.

In the developed world, the practice is usually to test for "total coliforms", some of which are fecal coliforms, and some of which are not. That is because water systems in the developed world can expect to keep out not only fecal waste, but soil. In the developing world, where soil is usually unavoidable, a total coliform test would be over "sensitive", and under "specific". In other words, it would tell us all water has some turbidity, which is not what we need to know. Instead, it is better to use a test for fecal coliforms, or a test for E.coli. Either would tell us (with acceptable accuracy) whether or not a water point is being exposed to fecal waste.

The DelAgua

Advantages

Disadvantages

Colilert

Advantages

Disadvantages

Pathoscreen Pillows

Advantages

Disadvantages

Burning questions

I would appreciate any comments on the tests mentioned above, or on other tests that I may not be aware of. I'm especially interested in comments about the possibility of using them, or "petri films", without an incubator. moirawalsh@tulanealumni.net

Links