TDS meters

Q: "How does a TDS meter work?"

• They have a pair of small metal probes that go into the water and are used to measure water's electrical resistance. This will always vary according to:
  • How pure the water is
  • The water temperature
• The TDS meter is able to calculate the water quality almost instantly by using this information, and show you a reading of purity on the screen.

Q: "What unit does the TDS meter use to show the purity of the water?"

• A TDS meter measures TDS, or 'Total Dissolved Solids' and then displays it to you as PPM, or 'Parts Per Million'.
• 'Parts Per Million' basically refers to any elements in water that are not the water itself. So if you got a little bit of water and counted out exactly 1,000,000 particles, or molecules, you would see that most of them are the water molecules and a few of them are not water. They might be other elements, such as calcium, chlorine, or some other chemicals just floating along in the water or dissolved into it. Does that make sense? So as an example (we are encouraged to practice using illustrations right?) you might make a glass of orange juice by putting a 1/4 of a glass or juice and 3/4 glass of water. Well if you were to carefully count out 1,000,000 molecules from the glass you'd find that for every 750,000 molecules of water there would be 250,000 molecules of orange juice. Sounds tasty!
• Therefore, when a TDS meter reads water and tells you that the reading is '010' PPM, what it's saying is that out of the 1,000,000 molecules of water it checked, 10 molecules are not water, and 999,990 molecules are water.
• Occasionally someone has a TDS meter that is reading micro Siemens (µS) instead of PPM. This is a measure of electrical resistance and is not immediately easy to understand. There are conversions to work out PPM from µS but it's easier to just use a meter that gives the PPM measurement from the beginning.

Q: "Are TDS meters accurate?"
Q: "Can TDS meters be trusted?"

• TDS Meters are very sensitive pieces of equipment and can read water purity very precisely.
• To get the most reliable results you should always take several readings in a row and see the average. Just be careful not to get the water on your hands when you are taking the water samples. This would corrupt the water by washing some impurities from your fingers into the water. Another common mistake is not to wash the cap and the meter in the water you are measuring. You might still be reading impurities from the last sample if you don't rinse everything off in the fresh water.
• The most accurate TDS meters are the handheld ones.
• The least accurate TDS meters are the inline ones. Why? Because often the water they are reading is stuck in a small dead end of the pipe. This means the water might be from a long time ago. For best results with an inline meter the probes need to be directly in the water flow.

Q: "Do TDS meters ever lose their accuracy?"
Q: "Is there a way to reset TDS meters?"

• They can do. This can be due to:
  • Getting water inside them (This is usually the end of the meter, even when they dry out they never work properly again)
  • Low battery (just change the battery!)
  • Losing their settings in some other way (Recalibrate the meter if that's an option)
• To recalibrate a TDS meter you need to have a liquid of exactly known PPM, ideally a high PPM. Then you put the meter into the liquid and adjust it until it reads the correct amount. That's why we sell calibration solution which has a reading of 342PPM and this is very accurately manufactured.

Q: "How do I calibrate my TDS meter?"

• Use the calibration solution and dip your meter into that liquid. If the meter shows something other than 342PPM then you have to adjust the meter until it does show 342PPM. The way you do this depends on the exact model of TDS meter you have. Not all can even be calibrated. But most will either be:
• Use a small screwdriver to adjust the meter through a tiny hole in the back of the body

Q: "Can a TDS meter be used to measure the purity of other liquids?"

• No! They are made only for water. Probably there do exist TDS meters for other liquids but our ones are only for water.