For the past few months, Rick and Dan have been dipping nitrate test strips when we collect water samples for the lab. We have confirmed that the reaction is temperature-sensitive, causing nitrate test strips to under-estimate nitrate concentrations in winter. Accuracy can be improved by testing a water sample in a warm car, or by allowing an extra 30-60 seconds for the color change, but for best results, follow Heather Wilson’s advice, reprinted below:
“Hach (the manufacturer of the test strips included in your Nitrate Watch kit) says that sampling will be most accurate when the sample temperature is between 20 and 25° C (68 to 77° F). These ideal temperatures are easy to obtain indoors, but much more uncommon outside.
If you are concerned about cold weather impacting your nitrate readings, we recommend collecting your sample in a clean container and allowing the water to come to room temperature before taking your nitrate reading. Make sure to rinse the container three times with water from the water source you are sampling to ensure that no residual water from past samples remains.”
-Heather Wilson, Midwest Save Our Streams Coordinator, Izaak Walton League