A colour change in the control vial indicates interference of a chemical in the water. The chemical is usually the waterline disinfectant/cleaner, for example chlorhexidine. If there are chemicals in your water, you can still use E|One accurately by performing an additional step. After collecting your sample, add approximately 10 mL of distilled water to the top of the T-Cup. Wash the sample by moving the top half in clockwise and counter-clockwise directions (by opening and closing the T-Cup). Throw out the concentrated water from the top of T-Cup. Continue with regular directions.

Note: The colour change in the control vial will be similar to the colour of normal results, therefore it is important to know your resulting colour is from the microorganism count, and not chemical interference.