Wow! I tested my reverse osmosis countertop filter and tap water with this tester, and the results were crazy. My tap water had over 600 TDS (total dissolved solids) and my reverse osmosis drinking water had only 25 TDS in the results. This tester also reads EC (Electrical Conductivity), and temperature. I like the larger screen and how easy it is to read. The tester is great for portability. I took it to work and tested the drinking water there. I think these would make great gifts and provide some answers to the people curious if their water filtration unit is filtering enough. Overall, I'm satisfied with the tester, but my tap water sure appears nasty with the results I got.