On 5 Dec. 2017 I performed a comparison of various water quality test kits on 3 water sources in Caiman Haiti. The goal was to see which kits are more suitable for teaching, and which are more precise in nitrate measurements. Water sources were an unprotected well used by village residents for washing and cooking, a university cafeteria outdoor sink used to wash dishes, and a household drinking water dispenser supplied by a reverse osmosis system (treated water) at the university. The sink water and treated water come from the same well. In summary, the Lamott and Waterworks kits that use plastic test strips are more convenient and have more precise lower chemical ranges than the kits that use dissolvable pills (LaMotte® Water TesTab® Kits). Also, the reverse osmosis system appears to reduce nitrates and phosphorus in the water.
Water samples were obtained 6:30 – 6:45am in sterile whirlpacks. Prior to the chemistry tests, sterile pipettes were used to place 1 ml of each sample on 3M petrifilm to determine presence of fecal coliform. Before each chemical test, vials were rinsed three times with the sample to be tested. All tests rely on the user differentiating color shades that represent gradations in the amount of chemical being tests. The Lamotte Testabs require vials and monitoring the time taken for the color to develop. Phosphorus tabs take longer to dissolve, while the pH tabs crumbled as I removed them from the packaging. Also, the ranges of chemical values are crude and too low for my purpose of testing drinking water. One can only get a range estimate which is a problem when testing a critical chemical such as nitrate (> 10 mg/l nitrate-N in drinking water is hazardous to infants). Also, the tabs measure nitrate as nitrate-NO3 which must be converted to nitrate-N to compare to USEPA drinking water standards. There is also the question of what to do with the used solution when one does not have a sink to wash it down. I have my students pour the solution into a tub which I then dilute and pour among vegetation away from the waterbody we are testing.
Plastic strip kits used were Lamotte Insta-Test (phosphorus, pH, and nitrate/nitrite), Waterworks (nitrate/nitrite), and SenSafe (chlorine). These are much simpler, and the only waste is the small plastic strip. However, the color changes quickly, so one must be ready with the container that has the color shades. This was a problem when I had only one container but had 5 groups of students test their water at the same time. I learned this when the phosphorus test continued darkening before I could reach all groups, thus giving values that were too high. This test requires the 10ml sample tube that is used for the Testab kits. The plastic strip is folded into the cap of the tube, then the cap placed on the tube, thus inserting the strip into the sample. After removing the cap and strip, one looks through the tube from the top to compare color, and it was difficult for me to distinguish shades. Also, nearby color, such as a shirt or notebook, can influence the color seen through the tube. The Waterworks kit has more precise ranges of 0, 0.5, 2 5, 10, 20, 50 nitrate-N ppm than Lamotte with 0, 5, 10, 25, 50 nitrate-N ppm, so I will save the former when testing wells, and use Lamotte in the classroom.