I’m testing the pH of RO, distilled, and tap water, but the test strips aren’t changing color. Are the strips not working or is my water off the charts?

When testing RO, distilled, or tap water, the strips may not behave like you would expect. The colors on the chart were developed for these strips using buffer solutions. The indicators used with the strips require that the waters being tested have some buffering capacity. RO and distilled waters have little or no buffering capacity, and the test strips will not work in these waters. If the tap water has a very low buffer capacity (low hardness, low alkalinity, etc.) the color can take much longer than the recommended 1-2 second immersion and 10-15 development time.