TDS Creep in Reverse Osmosis – What You Need to Know

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If you haven’t used your RO system for a while, it is a good idea to test the TDS levels when you start to use it again.

However, you might get a bit of a shock at the reading! This is called TDS creep.

Let’s look at what it is and how to get an accurate reading.

Key Takeaways

  • TDS creep refers to an inaccurate measurement of the TDS in reverse osmosis water due to the filter system not being used for an extended period of time.
  • The RO system not being used regularly causes the balance of TDS on either side of the membrane to equalize, giving a high TDS reading when first tested.

What Is Reverse Osmosis TDS Creep?

So, what is reverse osmosis TDS creep?

If a reverse osmosis system remains unused for a period of time, the pressure inside the RO membrane will equalize, leading to a balance in the levels of dissolved solids. When you then open your reverse osmosis faucet, the initial cup or two of water that comes out of the membrane may have a higher level of total dissolved solids. This is known as TDS creep.

To prevent higher readings caused by TDS creep, if the reverse osmosis filter system has not been used for a while, discard the first two cups of water before testing. If you have an RO tank, open the faucet and drain all the water. After refilling the tank, check the TDS of the freshly filtered RO water for the latest measurement.

blue reverse osmosis membrane

Should You Take TDS Creep in Reverse Osmosis Seriously?

Why should you take a TDS creep seriously? Because high levels of total dissolved solids on the membrane can cause scaling, clogging, and biological growth, damaging your equipment and shortening the lifespan of your reverse osmosis membrane.

It’s important to keep a close eye on TDS creep and take action as soon as you notice an increase in levels. If not treated promptly, it could lead to costly repairs and replacements.

Incorrect Testing Due to TDS Creep

TDS creep can lead to inaccurate testing of your RO water quality. This creeping increase in TDS results from the mixing of pre-filtered water and filtered water within the RO membrane.

To ensure accurate testing of the TDS levels in the reverse osmosis system’s filtered water, it is crucial to flush out any TDS creep by discarding the initial 1-2 cups of water before testing. This way, you can assess the actual performance of the membrane and not the water affected by TDS creep.

To test accurately, try:

  1. Disconnecting the RO membrane permeate output from the rest of the system.
  2. Allow the system to run.
  3. Set aside the initial water as it may exhibit higher TDS.
  4. Retrieve a cup of water from the tubing and perform a TDS test. This will provide an accurate reading for the RO filter (aim for under 50 ppm).

If you have any questions about TDS creep in reverse osmosis please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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