IDEXX Colilert 5-sample Geomean

The IDEXX Colilert 5-sample Geomean method helps check E. coli levels in water by testing five samples from the same location. Each sample is mixed with Colilert powder, poured into a tray or left in a bottle, and incubated for 24 hours. If E. coli is present, the sample turns yellow or glows under UV light. After testing all five samples, scientists calculate a “geometric mean” (a type of average that reduces the effect of very high or low numbers). This gives a clearer picture of overall water quality instead of relying on just one sample result.