If you’re getting a high TDS reading from your reverse osmosis system, you might be dealing with an issue known as TDS creep.
In this guide, we’ve defined TDS creep, discussed why it happens, and whether you should be concerned about this temporary TDS elevation. We’ve also shared some of our top tips for fixing the issue.
📌 Key Takeaways:
- TDS (total dissolved solids) creep is a problem in RO systems that purify water with short, quick cycles rather than over an extended period.
- You can fix TDS creep by running your faucet for around 1 minute and discarding the first two glasses of filtered water. For tank-based systems, you’ll likely need to drain the tank and start again.
- You can prevent TDS creep by installing a top-off system, using a booster pump upstream of the reverse osmosis unit to increase the flow of water passing through the RO membrane, and making your own anti-TDS creep device.
Table of Contents
🤔 What Is TDS Creep?
TDS creep is a term that describes what happens when a reverse osmosis system isn’t used for a short period, causing the pressure in the semi-permeable membrane to equalize and balancing the TDS levels.
As a result, when you switch on your faucet and test the first 1-2 cups of water, you’ll notice that the concentration of dissolved solids is higher than the usual TDS concentration in your RO water.
TDS creep is annoying, but it’s also easily resolved. Simply discard the initial glass or two of water (or use the water for other purposes, like watering your plants).
Once the initial higher-TDS water has been expelled, the TDS levels in the water should drop back to the normal level – as long as the system is working properly.
🔎 What Causes TDS Creep?
The most common cause of TDS creep is if your reverse osmosis system has short-duration, frequent cycles of water treatment.
If only small amounts of water pass through the RO membrane (for example, if the RO system is hooked directly to your sump), the system will produce poorer-quality water that’s higher in total dissolved solids.
Another factor that may cause or contribute to TDS creep and reduced RO water output is low water pressure in the reverse osmosis unit. This will reduce the flow of water through the semi-permeable membrane.
🧐 Does TDS Creep Affect Water’s TDS Reading?
Yes, TDS creep affects the TDS reading of reverse osmosis tap water. In fact, a randomly higher TDS reading, which decreases to a lower reading as you continue to dispense water from your RO unit, is the most obvious sign of TDS creep.
TDS creep may lead to incorrect testing of your purified drinking water quality. When you test water with a TDS meter, the TDS concentration will read higher in the first 1-2 glasses. To get an accurate reading, let your reverse osmosis faucet run for at least 1 minute before taking a reading. Compare your results to your pre-filtered water TDS.
🚰 Should You Be Concerned About TDS Creep?
No, TDS creep isn’t something to be concerned about. It doesn’t mean that your reverse osmosis membrane needs replacing or that your RO system is about to break down.
TDS creep is simply the result of using your RO system after a period of no use. While it may affect your RO water quality, it’s not a permanent problem, and it can be resolved in most cases by simply letting the water run before filling a glass.
With that said, TDS creep may cause high concentrations of TDS to damage the semi-permeable membrane, potentially reducing its lifespan. That’s why it’s a good idea to take action against this issue as soon as you notice it, to prevent the possibility of equipment damage and keep your RO system in good working order.
🔧 How To Fix TDS Creep
There are a couple of simple ways that you can fix TDS creep in your RO unit:
Discard Your First 1-2 Glasses Of Water
If you use an RO filter system without a tank, fixing TDS creep is easy: just fill 1-2 glasses of water and discard these initial water batches (which, due to TDS creep, will have a higher TDS reading).
Once the RO system kicks in and fresh tap water starts flowing through the filter stages, the TDS creep issue should no longer be present.
Drain & Refill The Tank
If you have an RO tank, you’ll need to completely drain the tank and refill it with pure water from the RO unit.
This will get rid of any water that has been affected by TDS creep, and the new water in the tank shouldn’t have this issue because the tank has been filled over one long period, rather than intermittently.
🚫 How Do You Prevent TDS Creep?
We couldn’t find any specific advice from manufacturers of reverse osmosis water systems on how to prevent TDS creep.
However, anecdotal evidence from various users suggests that the following methods should prove effective in preventing TDS creep:
- Use an auto top-off storage tank. Ensure that this tank is filled less frequently, rather than being filled gradually with frequent, short-duration cycles.
- Use a permeate pump/booster pump. This will increase the RO system’s efficiency and reduce its wastewater production.
- Use a DIY anti–TDS creep device. The aim of this device should be to allow the tank to fill in one cycle over an extended period, rather than refilling very small amounts every time you switch on your RO faucet.
Contact your reverse osmosis unit manufacturer for advice specific to your system.
📑 Final Word
TDS creep isn’t something that’s widely discussed, but it’s important to know about this issue so you can continue to get the best results from your RO filter system.
If your water is unusually higher in total dissolved solids, check that TDS creep isn’t to blame. Your initial filtered water quality may not be a reflection of the actual performance of the RO membrane, leading you to believe that the system is flawed – when actually, the problem is temporary.
Thankfully, the issue is easy enough to resolve – but you may need to adjust your system to allow it to run for longer periods, preventing an increase in the TDS coming out of the membrane for the initial minute.