How a Permeate Pump Works with a Reverse Osmosis System

Posted by
John Woodard on December 18, 2018

A permeate pump increases the efficiency and productivity of a reverse osmosis system. Without a permeate pump, a reverse osmosis (RO) system dispenses a lot of water to the drain and produces clean water at a slower rate. John Woodard, our Master Water Specialist, explains how this RO water pump can improve your reverse osmosis system.

What is a permeate pump?

A permeate pump is applied reverse osmosis (RO) system to save water sent to the drain and allow the system to operate at its highest efficiency. An RO system with a permeate pump produces a higher quality of water at a great flow rate. An RO with permeate pump installed saves up to 80% of the water to drain.

What is permeate in reverse osmosis?

In reverse osmosis, permeate is defined as the clean drinking water produced after RO membrane filtration. The permeate pump earns its name from its ability to speed up the production of clean water during reverse osmosis. 

The reverse osmosis membrane separates contaminants from the permeate water. The RO reject water (also called brine or concentrate) carries the contaminants away to the drain. The inlet and outlet of a permeate pump are labeled as "brine in" and "brine out" to show the separation of the potable water from the dirty water. 

How permeate pumps work

The permeate pump stores the RO reject water or brine in a chamber and uses it as energy to send the permeate to the RO storage tank. As the drain water collects in the pump, it activates a piston that pushes the permeate water into the storage tank. This process prevents the water pressure in the tank from pushing against the RO membrane, improving the system's performance.

A permeate pump has an inlet and outlet for the brine and permeate on each side. The brine supplies the energy needed to send the water to the storage tank. 

  1. "Brine in": Reject water from reverse osmosis collects on the left side of the pump.
  2. "Brine out": The brine supplies energy for the pump and then flows through the outlet to the drain.
  3. "Permeate in": Permeate flow from the membrane collects through the inlet.
  4. "Permeate out": The permeate exits the pump and heads to the storage tank, propelled by the energy from the brine. 

Permeate pump diagram

Permeate pump in a reverse osmosis system

RO permeate pump vs. RO booster pump

An RO booster pump increases water pressure when it's too low for the RO membrane to operate. Permeate pumps are not designed to boost water pressure or deliver water but to help reverse osmosis systems save water. An RO booster pump boosts water pressure, while the RO permeate pump makes reverse osmosis more efficient. 

Learn more about how booster pumps work.

Do you need a permeate pump?

Unlike many other pumps, a permeate pump requires no electricity to operate. Instead, it uses the hydraulic energy that would otherwise be wasted to prevent more water from going to the drain when the RO tank nears full. You receive 80% in efficiency by adding a permeate pump to an RO system and save gallons of water per year.

The Center for Disease Control considers reverse osmosis systems one of the best point-of-use home water treatment methods, but on their own they're not efficient. A permeate pump improves an RO system's efficiency by reducing the amount of water sent to the drain versus the amount of clean water collected in the RO storage tank. The permeate pump allows an RO system to use less water for optimal performance. 

Why an RO system needs a permeate pump

Reverse osmosis systems make water very slowly. For this reason, they come with a storage tank so RO water is ready to go when you need it. The tank is hydro-pneumatic, which means it has two chambers inside (for air and RO water) separated by a diaphragm. As water fills the tank, the air compresses, producing energy to push water out of the tank and send it to your faucet. This energy also creates resistance against the RO membrane, which slows water production. As production slows, the ratio of water to drain increases and the system loses efficiency.

The permeate pump creates a barrier between the tank and the RO membrane so the increasing pressure from the tank doesn’t affect production. It uses the water going to drain to power the pump to push RO water into the tank. This increases efficiency, maintains a low drain ratio, and allows the membrane to work at the optimum level of quality water production.

Imagine trying to get into a room, but someone is pushing against the door on the other side. You may be able to break through after much effort, but if you add more people on your side to help you, it's much easier. The permeate pump acts like that added force helping the membrane break through the resistance. 

Benefits of a permeate pump

  • Increased water quality
  • More consistent water flow
  • Faster storage tank fill
  • 85% less water sent to the drain
  • Powered by brine water
  • Easy integration with most RO systems

Saves water sent to the drain 

An RO system sends three gallons of water to the drain for every one gallon produced. But with a permeate pump, it maintains the same ratio of clean drinking water compared to drain water wasted from start to finish. 

Increases production

A permeate pump alleviates pressure on the membrane and allows the RO storage tank to fill faster. The pump also increases the amount of clean water produced by an RO membrane due to the enhanced efficiency.

Requires no electricity

Permeate pumps use RO reject water for energy rather than electricity. They collect the dirty water headed to the drain and use that energy to push the permeate water into the reverse osmosis storage tank until you need it.

How much does a permeate pump cost?

Aquatec permeate pumps range from $30 to $100 depending on the gallons of water produced per day. Before buying a permeate pump, make sure your RO system is designed for one. If you're a first-time RO customer, look for a system that comes with a permeate pump, like the Neo-Pure deluxe system, or one that's plumbed to include one. 

A permeate pump with or without ASO

A typical reverse osmosis system uses an automatic shutoff (ASO) valve to stop water production before the storage tank is full. As water fills the tank, air pressure rises and pushes more water down the drain. The fuller the tank gets, the amount of water to drain increases. 

A permeate pump with a shut-off valve stops water from entering the storage tank when it reaches 2/3 of its incoming pressure, which reduces the water pressure at your faucet. A permeate pump without a shut-off valve allows water to fill the storage tank and supplies water at maximum pressure. You do not need an ASO valve with a permeate pump, but having both may help prevent TDS creep.

How to install a permeate pump

A permeate pump is labeled with "brine in" and "brine out" and "permeate in" and "permeate out," to help you know where to insert the tubing.

  1. Screw a mounting clip to the manifold.
  2. Insert the pump into the clip with "brine out" and "permeate out" at the top.
  3. Insert the pump inside of the clip.
  4. Turn the RO system around.
  5. Remove the tubing from the permeate port of the membrane housing.
  6. Disconnect the other tubing end from the ASO valve.
  7. Insert new 22" tubing into the permeate port of the membrane housing.
  8. Bring tubing to the front of the system.
  9. Insert the tubing into the "permeate out" port.
  10. Attach an elbow stem fitting into the "permeate out" port.
  11. Insert 15" section of tubing into the fitting.
  12. Attach the end of that tubing to the ASO valve.
  13. Locate the flow restrictor.
  14. Insert 22" tubing into the flow restrictor.
  15. Direct the tubing toward the front of the system and weave it through the holes in the mounting clip.
  16. Place an elbow fitting on the end of the tubing.
  17. Insert the tubing into the "brine in" port.
  18. The "brine out" port connects to the drain line.

You can easily install a permeate pump on some, but not all, reverse osmosis systems. Compact manifold RO systems with three or four tubing connections are the exception. Like a check valve, the permeate pump only lets water flow in one direction. In most manifold systems, water must enter and exit the tank through the same line. To install the pump on this type of system, you'd have to bypass the postfilter.

If you have questions about your reverse osmosis system and whether or not a permeate up will hook up to it, give us a call at 864.284.1801.

Comments 1-5 of 5

We have had the same RO system for 20+ years and it works fine. It’s exactly like the one in your picture for installing the permeate pump retrofit kit. About 10-12 years ago I added your permeate pump and it, too, works fine. I change all filters in the system about every 12-15 months (there’s just 2 of us). After changing all the filters and few months ago we seem to have noticeably less RO water volume produced than before even though our usages has not changed. It just seems to take longer to produce a similar volume of RO water than it used to. The permeate pump is working because I hear it clicking.

Any troubleshooting suggestions or answers as to why we’re getting RO water at a slower rate ?

Roger on August 25, 2022

Excellent video. Question: We’re on well water, which due to using a large bladder storage tank, the incoming water pressure can fluctuate from +35 PSI to about 60 PSI (pump starts at around 35 and turns off around 60). I’m using a RO booster pump to boost pressure of the RO filter. Will the RO benefit by installing a permeate pump even though it has a booster pump installed?

FELIX I OQUENDO on May 20, 2022

Installed a reverse osmosis system which came with the permeate pump, unlike the previous system, this new system has the most annoying clicking sound which did not exist with the previous system. Two questions: is there a permeate pump that is quite? Could this pump be removed, or, bypassed? Please let me know. Thank you very much.

WILLIAM on October 08, 2021

Will this permeate pump work with AO Smith AO-US-RO-MB-4000?

Per Hagstrom on April 06, 2021

I have been using a permeate pump from you for a couple years and recently moved my RO system to the basement. i want to add an electrical booster pump (aquatec 6800) to the system to get better pressure upstairs but want to be sure that it can be used with a permeate pump together. Also, where should the booster pump go in the system?

Jason Baker on April 06, 2021
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