3M Petrifilm plates

The 3M Petrifilm method is a way to measure E. coli levels in a water sample using a special plate. A set amount of water is placed on the plate, which contains a gel that helps bacteria grow. The sample spreads across the surface, and the plate is kept warm for about 24 hours. If E. coli is present, blue colonies with gas bubbles form on the plate. By counting these colonies, scientists or testers can estimate the amount of E. coli in the water. This method is commonly used for simple lab tests, including at-home water quality checks.