TDS stands for Total Dissolved Solids. It is the measurement of all the dissolved substances in a water sample. These “dissolved solids” are mostly inorganic salts like sodium, calcium, magnesium, and potassium cations along with chloride, bicarbonate, carbonate, phosphate, sulfate, and nitrate anions.
Truly accurate TDS measurements must be performed in an analytical laboratory. The water sample is weighed and then heated under tightly controlled conditions to evaporate the water. The remaining weight of the leftover “solids” is used to calculate the TDS in the water sample. However, this level of accuracy is not necessary for most at-home testing applications. It is expensive and must be performed in a qualified laboratory. Using a TDS meter is a much faster and affordable method.
Why is the TDS important?
Let's make this clear - TDS is not a measurement of harmful substances or pollutants. TDS is simply a measurement of all substances dissolved in water. Distilled water has a TDS of 0.0 ppm, while the ocean has a TDS of 10,000 ppm. Both water sources are "safe". An acceptable TDS is relative to the water being tested and what the water is used for.
Here is an example: If you tested the TDS of distilled water and found it to be 300 ppm, you would know that the water was not distilled. Perhaps the water purification system was faulty, or something had contaminated the distilled water. So, TDS testing is like a watchdog. It will tell you if things are not as they should be.
How do TDS meters work?
TDS meters do not directly measure the total dissolved solids. Remember, the TDS is determined by evaporating the water and weighing the remaining solids. Instead Hand-held TDS meters measure electrical conductivity (EC). Dissolved inorganic substances like salts and minerals conduct electricity. The higher the concentration of these substances in the water sample, the higher the electrical conductivity. A TDS meter performs a few calculations based on the EC value to arrive at an estimated TDS reading. This is what you see on the screen.
The great thing about this meter is that it works for almost any type of water testing you have in mind:
RO, DI, or distillation unit effectiveness
Nutrient levels in a hydroponic setup
TDS in swimming pools, spas and hot tubs
Aquariums and fish tanks
And many more
However, there are also some applications where a TDS meter is not a suitable device for testing. These include general drinking water filtration systems, water hardness, and saltwater aquariums for example. You can find out more about this in the FREE User Guide below.
When to calibrate your meter?
Your TDS meter is factory calibrated (at 342 PPM), so you can use it straight out of the box. However, if you wish to re-calibrate it, check the instructions in your product manual. Here's when you might want to consider calibrating your TDS meter:
After prolonged usage, recalibration may help to increase the meter’s accuracy.
TDS meters are more accurate when calibrated at levels that are close to the sample being tested. So, if you’re measuring samples that are around 1000 ppm, for example, it’s recommended that you calibrate the meter for that specific value.
Helpful Resources and Downloads
The instruction video is currently being filmed and will be uploaded shortly.
If you want to learn more about your drinking water or how to take care of it, theU.S. EPA website is a great resource to look up.
Frequently Asked Questions
The only drinking water filters that have an effect on TDS are reverse osmosis (RO), distillation, or deionization filters. The Zero water filter is another word for a deionizing water filter.
No other type of filter will significantly reduce TDS. However, you can measure TDS on any drinking water source to get an idea of the TDS level.
Yes. Water treatment professionals use our TDS meter to monitor the status of the RO membrane in home and commercial filter systems. You can do it too.
First, measure the TDS of unfiltered water. Then measure the RO water. The RO should be removed at least 90% of the TDS. Most people replace the RO membrane when the RO removes about 70% of the TDS.
If your RO has an activated carbon post-filter, it may add some minerals back into the RO water. This can increase the TDS a little bit when the post-filter is first put into service.
Yes. The meter displays both °F and °C
77°F (25°C). This is the universal temperature for calibration.
1 x 3V Button Cell CR2032 (can be easily replaced) .
No. This meter measures total dissolved solids (TDS) only.
While water hardness is a component of the total TDS measurement, it is not a water hardness test. ppm TDS is not the same as ppm water hardness. A water hardness test kit is designed for measuring calcium and magnesium minerals only.
If you need water hardness test strips, you can find the Health Metric test strips here.
No. Water hardness minerals are detected by TDS meters, along with will all other minerals and salts. Also, ppm TDS is not the same as water hardness ppm. They are different parameters. You need the Health Mettric water hardness test strips for this!
Yes. The meter is perfect for measuring nutrient solutions. Note! This meter reads EC in microsiemens (uS). Some hydro fertilizers use millsiemens (mS). 1000 uS = 1 mS.
Yes. It is fast and easy. The instructions come with the meter.
After each use, rinse the probe in clean or distilled water. Then let the probe air-dry.
No. TDS meters work by measuring electrical conductivity and converting it to TDS. Since distilled water won't conduct a current it will always read zero ppm, even if the meter is not calibrated properly. You must calibrate using a calibration solution based on its NaCl level.
No. You'll need a specialty TDS meter that can read over 10,000 ppm. A refractometer is more accurate and easier to use for this particular application.
TDS and salt meters are essentially the same meters. They work by measuring electrical conductivity (EC) in water. EC is converted to either TDS in ppm or an estimated salt level in ppm. A salt meter just runs the calculation for you and displays the estimated salt level as ppm.
However, salt meters don't really sense and measure the actual pool salts. It is all based on EC, which is influenced by minerals in the water, certain pool chemicals and the salt you add. Any salt meter, hand-held, at a pool store, or on your system is just estimating salt by measuring EC.
Correct. It uses the NaCl conversion factor. Look for the NaCl TDS level on the calibration solution when calibrating the meter. Ignore the KCl or 442 conversions, which are also present on most calibration solutions.
The only type of water filtration that lowers TDS is distillation, reverse osmosis or deionization. Carbon filters, Berky filters, sediment filters, water softeners, and other devices have no significant TDS reduction.
Bottled water is a generic term for water packaged in plastic or glass. Many types of bottled water come from the same source as your tap water - underground water supplies. The water may contain minerals and salts that are required to provide taste to the water.
Bottled water is not the same as distilled water. Only distilled or reverse osmosis water will have a low or zero TDS level. Remember, TDS is not a measure of "toxins." It is simply the measure of the minerals and salts dissolved in water. Good or bad TDS is relative to what you are using the water for.
Berkey filters remove sediment, fine particles and taste and odor-causing chemicals like chlorine and chloramine. It will remove musty odors caused by natural organics like geosmin.
However, this filter does not remove a significant amount of dissolved inorganic salts and minerals like sodium, nitrate, calcium, etc. Therefore you should see little or no reduction in TDS with this type of filter.