The RTS LS310 6-in-1 Drinking Water Quality Tester. It is extremely useful and very accurate. If you want high-quality distilled water, this device is excellent for testing water quality.
It measures TDS, COD, TOC, EC, temperature, etc., and the readings are reliable. The color screen is clear, the detection ranges are wide enough for everyday and more demanding tests. Very well made, and good value for the precision you get.
If you care about drinking clean water, this tester will give you confidence in knowing exactly what is in your water. Highly recommended.