Test vials need at least the minimum time mentioned above to show accurate results for the limit of 500 cfu/mL. Highly contaminated water will show a clear, colourless result within the minimum noted times. If at these times, your test vial is still pink, you can incubate for an additional 15 or 30 minutes to ensure an accurate result. This would be helpful for test results close to the 500 cfu/mL limit. Leaving the vials to incubate for longer periods of time will confirm a result.