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The Truth About Permeate Pump Reverse Osmosis Systems

by Mark Timmons November 08, 2011 96 Comments

At US Water Systems, we have been believers in Permeate Pump Reverse Osmosis Systems for over 10 years now. With several thousand permeate pump reverse osmosis systems in the field, we believed we were experts on these types of reverse osmosis systems. However, over the past year or so, we have become somewhat disillusioned with the permeate pump reverse osmosis system because we have had mixed results, primarily with poor water quality. Case-in-point: I always try different reverse osmosis systems at my home and after trying the nextRO for several months, I replaced it with a permeate pump reverse osmosis system (50 gpd membrane). For your information, my TDS (Total Dissolved Solids) are around 540 ppm. After 8+ months, I was really discouraged because my TDS routinely remained at over 100 ppm. If I drained the system on back-to-back days, I could get it down below 50 ppm, but it would rise quickly again. TDS creep was winning the game. In case you don't know what TDS creep is, it is defined as follows:

"The natural diffusion of TDS ions through the membrane from the feed side to the permeate side when the feed pressure is shut off (i.e., when the tank is full). This effect results in lowered water quality." - A Practical Application Manual for Residential, Point of Use Reverse Osmosis Systems by Robert Slovak

Now, before we go any further, it needs to be understood that a permeate pump reverse osmosis system should do the following:

  1. A Permeate Pump RO should make water faster than an ordinary RO
  2. A Permeate Pump RO should make higher quality water than an ordinary RO
  3. A Permeate Pump RO should waste about 80% less water than any ordinary RO
  4. A Permeate Pump RO should deliver the highest pressure at the faucet of any RO

Well, my pressure was good. Excellent actually, as I was feeding two ice makers, a kitchen faucet and a humidifier. It makes water very rapidly and I know that it wasted less water, but the water quality was horrible. Additionally, we have several customers who were not thrilled with their water quality, just as I wasn't. What to do.... Everyone told me that the Aquatec 1000 Permeate Pump was the "cat's meow" but the results were less than stellar. After months of fighting this issue, I decided to try the "old Aquatec 500 Series Permeate Pump" which is designed for membranes up to 50 GPD. Not a 75 GPD or a 100 GPD, but just a 50 GPD. So, I changed the permeate pump ( a 2 minute job). Then I drained my reverse osmosis tank (the TDS was reading 114 ppm). When I got up the next morning I checked the TDS and it was 18 ppm! From 540 ppm to 18 ppm... not bad. It has remained below 25 ppm since then and we have made a decision at US Water: We sell a 50 GPD permeate pump with an Aquatec 500 Series Permeate Pump, not a 1000 Series. Here's what bothers me: Why can't the engineers at Aquatec (who makes the permeate pump) and Watts (who USED to make our permeate pump RO system) figure this out? All 50 GPD Permeate Pump Reverse Osmosis Systems from US Water now have the Aquatec 500... and exceptional water quality. This is a public service announcement brought to you by The Water Doctor! Oh... the 500 is also quieter than the 1000... duuuuhhhhhh!


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96 Comments

November 29, 2020 Mark Timmons

A booster pump ahead of the RO. A permeate pump is not of use here.

December 21, 2020 John

If I place a shut off solenoid valve right after the R/O filter, and it shuts off immediately when the booster pump stops, wouldn’t that stop tds creep?

December 21, 2020 Mark Timmons

Yes, it would!

April 11, 2021 FS

I’m considering your 6 stage filter setup in either the 50GPD or 100GPD. On our old system I think we were using roughly 4-5 gallons per day. I may want to go with the 100GPD system since I sometimes use the water for other things and want quicker water. My question is, should I be using the ERP-1000 for certain if I go with the 100GPD unit? Seems like so many people say the ERP-500 is a better unit, built better, and much quieter. I realize the capacity is lower on that unit. So is it worth going with the 50GPD unit to get the ERP-500 for those supposed benefits? I’m planning to install the system in my unfinished basement right below my kitchen so some extra clicking noise may not even matter as long as the ERP-1000 runs efficient and does its job.
Any help on deciding on the 50GPD or the 100GPD and being paired with the appropriate permeate pump. Thanks.

April 18, 2021 Mark Timmons

You can use either pump, but with a 100 GPD membrane, you will get more TDS Creep!

August 15, 2022 Hulya

Hi. Very interesting and enlightening article. I’m a little confused though! Are you now using 2 permeate pumps alongside each other or a 50 GDP RO membrane with an Aquatec 500 series permeate pump designed for membranes up to 50 GDP?

Also, my water pressure is quite good but I keep reading that a booster pump helps RO systems work better and prolongs the life spans of RO membranes as well as the whole system. So, should my RO system have both booster and permeate pumps together?

I have one more question, if you don’t mind, about hard water. Mine is quite hard. Any suggestions for this. Is it that I should select a particular RO membrane or something else is the answer to my issue?

I’d very much appreciate your time..

September 06, 2022 Mark Timmons

Use a 500 Permeate Pump for a 50 GPD Membrane and a 1000 for a 100 GPD Membrane. In the realm of importance, the single best thing you can do to improve RO performance is to feed it with soft water. Hard water contains calcium and magnesium, which creates scale on a RO Membrane, inhibiting its performance. Soft water contains sodium which does not form scale and is in fact, what RO was created to remove. For the highest quality water, I would use a booster pump with a shutoff switch, such as this: https://www.uswatersystems.com/aquatec-cdp-6800-booster-pump-with-transformer-switch.html. You need not use and ASO or the pereate pump.

January 26, 2023 Aleks

Do you have a diagram of how to install the P/P with an ASO, on the All American 6-stage? P/P for the efficiency, ASO to keep water quality highest (even at the sacrifice of some pressure)

February 02, 2023 Mark Timmons

Call our Tech Support Department at 800-608-8792, and they can provide it. We do need a little more context.

March 19, 2023 Brian

Hi Mark, do you mean real soft water post salt softener? or would a non-salt softener or one of those electronic descalers be good enough too? thanks for your help!

April 11, 2023 Mark Timmons

The electronic descalers work as well as a Star Trek Transporter. That’s real isn’t it (sarcasm alert).

October 16, 2023 Cody H.

So a 75-100 GPD RO system, needs to be “downgraded” to a 50 GPD permeate, so it is not sitting idle and getting diffusion accross RO membrane? I assume that is only when light use? Ie restaurant scenario, this would not be an issue; being used more? Sounds like we are back to the age old, size for your need? Kinda like running too large an engine…the light load does not keep everything “seated” as well! Could your tech support, please comment on how to size now, with this experience?

November 07, 2023 Mark Timmons

TDS Creep occurs when you only use a fraction of your storage tank’s capacity at a time. For example, let’s say your storage tank holds three gallons. Maybe you make a pot of coffee in the morning, and then several glasses of water are drawn. If that is your daily use, then you will get tDS creep. In a restaurant, you would likely have a larger tank and use more water. If your tank holds 12 gallons and you fill up pits and carafes all day long, then that would not be an issue, but if you are taking glassfuls out, one at a time, that is an issue!

November 07, 2023 Charles Leo

I don’t know where or how the term “TDS Creep” came from but I think it’s less of a creep and just a simple function of essentially forcing more water through a RO membrane. If I’m correct in my thinking about how this operates, the permeate pumps functions similar to an alternativing check valve which reduces the flow of the brine (waste) heading out to waste. PMs exert more pressure by squeezing/forcing the water through the RO membrane instead of just hitting the membrane and dumping down the drain. The additional pressure on the RO membrane as a result “spreads” the membrane to a small degree (think of it as a very fine sponge) due to the increased pressure and you’ll find more Total Dissolved Solids (TDS) in your product water (the final output.) I just think this trade-off is the nature of installing these permeate pumps. If you install one, expect to see an increase (hopefully slight) in the TDS. I think it’s completely wrong for people or companies to say that these pumps increase the quality of the final product water—they don’t. Instead they will increase the TDS in most cases slightly. They also exert more strain on the RO membranes so they’re not going to make the filters last longer. If anything it makes the RO membranes work harder. HOWEVER, the pros are that they greatly reduce water waste, they fill up tanks faster, and due to the increased pressure it results in faster flow to faucets and ice-makers. So I think if you’re willing to live with some of the cons (I am), then the pros outweigh them. On a related note, I read one comment in which a person was saying they had to replace their pumps regularly. I have to wonder what their input water TDS is to begin with. I can see this happening in areas where the water quality is terrible (high TDS) which could quickly gum up the pumps. On the other hand, if you have mediocre or better water to start with (under 500 TDS), I’d imagine these pumps could last a lot longer. The only other thing I would add about filtration in general is that people SHOULD replace these filters when the manufacturers tell them that they should. I know it’s a tendency for many os us to either try to save money (like me) or think that these companies just want to make more money, but the truth is that these filters will degrade rapidly and that the particles they release once that starts happening can be worse than the cure. So do yourselves a favor and don’t skimp on those filter changes.

November 07, 2023 Mark Timmons

No, TDS Creep is an actual phenomenon that occurs under the conditions described. You can read any primer on Reverse Osmosis and know this to be true.

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