Plan membrane change with TDS meter
A TDS meter is a very useful tool for owners of reverse osmosis systems. Using the reading provided by the TDS meter, in conjunction with a reference value, you can monitor the efficiency of your system and thus plan, for example, a membrane replacement. We'll be happy to explain exactly how this works here.
What does a TDS meter do?
First, some basic information about TDS meters. These devices measure the content of dissolved solids (e.g., salts, metals and heavy metals, minerals, and many others) in all kinds of solutions, including water.
The measured value indicates the number of dissolved, ionized solids (particles) per 1 million measured parts (unit ppm = "parts per million"). This means that at a value of 20 ppm, there are approximately 20 molecules of other particles for every 1 million water molecules. The measuring devices measure the electrical conductivity of these substances and then convert it to ppm. This value can also be referred to as electrical conductivity and is expressed by some measuring devices in µS (micro-Siemens).
What a TDS meter cannot measure, however, is the concentration of specific pollutants in the water. The measured value is not suitable for this purpose, as it only provides information about the number of the dissolved parts, not but their type or components.
How do I use a TDS meter with my system?
Measurements with a TDS meter are useful when maintaining your reverse osmosis system. The measured value is particularly useful as a guide for when the membrane needs to be replaced. All you need is the measured value of the filtered water and the reference value of the unfiltered water. The retention rate of a good membrane is 90-95%. Here's how to measure it:
You turn on the faucet, let it run for a few seconds, and then fill a glass of water. You insert the TDS meter into the water and press the measurement button. This determines a TDS value of, say, 450 ppm for your unfiltered tap water. The filtered reverse osmosis water (after two minutes of running) has a value of, say, 45 ppm – meaning 10% of the original particles are still present in the filtered water. The membrane thus has a retention rate of 90%.
Conversely, if tap water contains, for example, 610 ppm, a membrane change would be necessary if the filtered water contains more than 61 ppm.
As mentioned, a good reverse osmosis membrane achieves 90 to 95% retention of the substances present in the water (filter performance). A guideline value of 10 percent dissolved solids is therefore within the acceptable range, and the membrane would not necessarily need to be replaced until the next measurement.
If your calculated result is above 10%, you should plan to replace the membrane as soon as possible. You can also perform these measurements if you notice unexpected changes in the taste of your filtered water. If the result is within the normal range, the membrane can almost always be ruled out as the source of the problem.
How often should I take these measurements?
We recommend measuring twice a year at least from the third year of use. As a rule of thumb, reverse osmosis membranes should be replaced every three to five years. TDS measurements help determine this timeframe more precisely.
