Comparison and verification of four field-based microbiological tests: H₂S test, Easygel^®, Colilert^®, Petrifilm™

The UN defines water supplies as ‘improved’ or ‘unimproved.’ These indicators are easy to measure, but do not reflect water quality, which requires laboratory or field tests. Laboratory and test availability, expense and technical capacity are obstacles for developing countries.

This research compares and verifies four low-cost, field-based microbiological tests: the EC-Kit (Colilert^® and Petrifilm™ tests), the H₂S bacteria test, and Easygel^®, against a standard method (Quanti-Tray^®). The objectives are to: (1) verify the accuracy of the four field-based tests, (2) study the accuracy of these tests as a function of improved and unimproved sources; (3) recommend a single microbiological test, if appropriate, based on accuracy and cost, and/or (4) recommend a testing combination, if appropriate, based on accuracy and cost.

The tests of 500+ total water samples from Capiz Province, Philippines and Cambridge, MA indicate that two-tests systems gave better results than a single test. Both the 100-mL H₂S test + Petrifilm™ and the 20-mL H₂S test + Easygel^® combinations yield promising results, in addition to being inexpensive. None of the field-based tests should be used on their own. We recommend further verification of a larger sample size and scale be undertaken before these testing combinations are recommended for wider use.