TDS meter provide you with the tools required to detect the total amount of dissolved solids in water. Dissolved solids can include minerals, salts, calcium, magnesium, potassium, sodium, bicarbonates, chlorides, sulfates and other organic matter. TDS testers will not provide you with a reading on what chemicals or contaminants are found in water.

How a TDS Meter Works

Because the dissolved solids have an electrical charge, the TDS meter can measure the electrical conductivity.  It does this by emitting a small electrical current that passes through the water.  The meter then captures electrical conductivity, or EC and converts it into a TDS number.  Some meters are designed to provide both the actual EC reading and the TDS value.

TDS Levels

The dissolved solids found in water does not necessarily mean the water is unsafe but it does provided you with an indication of further testing is required or not.

  • High Levels of Dissolved Solids: Can be caused by hard water which is caused by  high mineral content and this can cause the water to taste or smell off.
  • Medium/Low Levels of Dissolved Solids: Typically a result of water purification.
  • Extremely Low Levels of Dissolved Solids: Could be problematic as it can be associated with corrosion and impact pH levels making the water acidic and corrosive.

Total dissolved solid levels will vary depending on the type of water being tested, area of the country you are in and source that the water was taken from.

TDS in Drinking Water

The dissolved solids that are typically found in drinking water come from a number of sources.  Many are natural and seep into water through the soil, but some come from pipes, sewage, and chemical run-off.  The amount and type of solids in your water can affect the hardness and taste.

The EPA has labeled TDS as a secondary contaminant that has an aesthetic effect. These are contaminants that can cause the water to have an unpleasant look, taste, or smell, but they are not considered a health threat.  The EPA has set the maximum contaminant level for TDS in drinking water at 500 parts per million, or 500mg/L.  The noticeable effects when levels exceed that threshold include hardness, colored water, deposits, salty taste, and staining.

How to Use a TDS Meter?

This is a simple but very reliable tester that measures the Total Dissolved Solids (TDS) in water. It gives a reading in parts per million (ppm) of all the dissolved solids, good or bad. Dissolved solids in water are mainly its mineral content. If your tap water, for example, has a TDS reading of 250 parts per million, that means that the total content of the minerals dissolved in the water make up 250 parts per million of the total volume.

For practical purposes, TDS measurement is a very effective way to test you reverse osmosis unit’s performance.

To operate:

  1. Remove the cover from the bottom of the tester, then turn on the unit by pressing the On/Off button. The display should read 000.
  2. Insert the tip of the tester (the end where the cover was) into the water to be tested. A half inch or so deep is plenty. You’ll ruin the meter if you submerge it too deeply.
  3. Read the numbers on the display. The number you see is the TDS (Total Dissolved Solids) of the water expressed in PPM (parts per million).
  4. The Hold button and the Temp button are features you probably won’t need. Hold locks the number on the display so it won’t go away and Temp measures the temperature of the water.
  5. When you’re finished, turn the tester off.

Note: The tester is factory calibrated. You won’t need to calibrate it.

Testing your RO membrane:

Measure the TDS of your tap water, then measure the product water for comparison. The RO water should be about 1/10 or less the reading of the tap water. In other words, if the tap water reads 250, the reverse osmosis water should read around 25 or less. What you are measuring is the performance of the reverse osmosis membrane. As long as you get a respectable TDS reading, the membrane does not need to be replaced. Typically, reverse osmosis membranes last three years or longer.