How a Permeate Pump Works in a Reverse Osmosis System

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 installed in a 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 greater flow rate than a system without a permeate pump. Permeate pumps save up to 80% of water that would normally flow to the 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" – Propelled by the energy from the brine, the permeate exits the pump and heads to the storage tank,. 

RO permeate pumps vs. RO booster pumps

An RO booster pump increases water pressure when it is too low for the RO membrane to operate. Permeate pumps are not designed to boost water pressure or deliver water. Instead, they 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: What is a reverse osmosis booster pump?

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 is nearly full. You receive an 80% increase in efficiency by adding a permeate pump to an RO system and save gallons of water per year.

The CDC considers reverse osmosis systems one of the best point-of-use home water treatment methods, but they are not efficient on their own. 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 pump allows an RO system to use less water while achieving optimal performance. 

Why an RO system needs a permeate pump

Reverse osmosis systems make water very slowly. The treatment speed of RO is so slow that a storage tank must be used to make RO water available when you need it. The tank is hydro-pneumatic, which means it contains a diaphragm that separates two chambers, one for air and one for RO water. As water fills the tank, the air compresses, creating 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, preventing the increasing pressure from the tank from affecting production. It uses the water headed to the drain to power the pump. With the hydraulic energy of the wastewater, the pump pushes the treated 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 an added force to help the membrane break through the resistance. 

Benefits of a permeate pump

Permeate pumps provide the following benefits to reverse osmosis systems:

• Increases water quality
• Makes water flow more consistent
• Fills storage tank faster
• Sends less than 80% of water to the drain than RO systems without a permeate pump
• Uses brine water to power pump
• Integrates easily with most RO systems

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 are a first-time RO customer, look for a system that comes with a permeate pump, like the Neo-Pure PRO-4 Series, or one that is plumbed to include one. 

Shop All RO Systems

Do permeate pumps need an 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. Follow the steps below to install a permeate pump into your system.

1. Screw a mounting clipto 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 tubingfrom 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 fittinginto 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. Connect the drain line to the "brine out" port.

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 would need to bypass the postfilter.

If you have questions about your reverse osmosis system or whether or not a permeate up will hook up to it, please do not hesitate to contact us.