Calibrate the conductivity meter with calibration solution. Use a calibration solution that has a conductivity near that of the water you are sampling. Adjust the meter to the appropriate reading using the calibration screw on the meter. Then rinse the probe or sample cup with distilled water. Remove any excess water.
Collect your sample in water bottles that are new or have been thoroughly cleaned and rinsed with distilled or deionized water. Laboratories that analyze water samples will provide you with sample bottles. Check the conductivity of the solution. Rinse the probe with sample water before testing its conductivity. Then, take the sample to the laboratory for analysis.
Take the result of the TDS analysis and calculate a conversion factor. Divide the value for TDS (in parts per million, ppm) by the conductivity value in micromhos or microsiemens. For instance, if the TDS analysis shows that your water sample has 250 ppm of total dissolved solids and the water conductivity is 600 micromhos, then the ratio with be 250 / 600 = 0.42. This conversion factor will work for a range of conductivity measurements for your particular type of water.
Things You Will Need
- Clean sample bottle
- Conductivity meter
- Conductivity calibration standard
- 1. Conversion factors may be similar for waters within a given region, but you must know the TDS values first before making a general conclusion as to what value to choose.
- 2. If you need to convert from micromhos to microsiemens, the standard SI unit for conductivity, the values are equivalent. For example, 400 micromhos is 400 microsiemens.
- 3. If you are testing hydroponics water which has fertilizers, then send a sample of the water to a laboratory for analysis. The fertilzer composition will change the conversion factor that will apply to the tap water.