If you’re a reverse osmosis (RO) system user, you know it’s one of the most effective methods for obtaining safe drinking water.
However, you’ll also know that a significant drawback to this technology is the amount of wastewater it produces.
RO systems can waste between 3 to 20 gallons (11-76 liters) of water for every gallon (four liters) of clean water produced.
Although wastewater from a reverse osmosis system is almost unavoidable, seeing those figures, you’d want to reduce it as much as possible.
This article is here to help you with that. So, let’s get started!
How Do I Reduce Wastewater From a Reverse Osmosis System?
To reduce wastewater from a reverse osmosis (RO) system, replace older models with newer, more efficient ones.
If you can’t replace your system, install permeate pumps or use membrane upgrade kits. You can also reuse the wastewater or ensure the pressure levels are optimal.
In RO systems, waste, concentrate, or brine water refers to the water discharged by the system as it contains a higher concentration of solids.
Such high concentration makes them unsafe for drinking or even bathing, but that does not mean you must throw them right away. Instead, you can reuse them for other purposes.
However, before reusing your RO system’s wastewater, check its total dissolved solids (TDS) level first.
TDS is the concentration of minerals and salts – such as calcium, carbonates, and magnesium – present in the water. According to Safe Drinking Water Foundation, water with a TDS level (per liter) of 900 or below has an excellent rating.
Above those levels, you may consider using them for other purposes, such as:
- Watering plants – plants benefit from the excess minerals and salts present in RO waste water. However, you must carefully monitor the plants you gave RO wastewater because some extra minerals, like fluorine, may harm them.
Sticking to below 2,100 ppm TDS levels is also best, although the recommended limit is 800 ppm.
- Wash your car – you don’t need potable water to clean cars. Thus, using RO wastewater is a good idea as you can kill two birds with one stone—a squeaky clean, shiny car and avoid wasting water.
However, for a car wash, it’s recommended to use wastewater with a TDS level of below 1,500 ppm. If it’s higher than that, dilute it with tap or clean water.
- Household chores – an excellent use for RO wastewater is mopping surfaces and cleaning utensils. TDS levels aren’t particular for these chores, but it’s best to stick to 2,000 ppm and below because if it’s higher than that, there’s a great chance of salt stains.
You can also dilute the wastewater if it’s above 2,000 ppm.
- Laundry – it’s recommended to use RO waste water for pre-rinsing. However, only use it for non-delicates.
Otherwise, the high concentration of minerals can damage the sensitive fabric.
- Toilets – you can use RO waste water for cleaning and flushing toilets. However, like household chores, use water with TDS levels of 2,000 ppm or below, or dilute them before use.
Porcelain is susceptible to salt stains and deposits; keeping the TDS as low as possible helps minimize those.
You can collect RO waste water by directing the drain line to pour into a bucket, or, like in this YouTube video, in a water container with a spigot for easy use:
However, if your RO system is bigger than the one in the video, consider getting a storage tank or rain barrel instead of a bucket or small container.
Whichever container you use, consider getting a spigot or hose attached because it would make it easier to reuse the collected water anytime you need it.
If you can’t use a spigot or hose, a submersible pump and water pipe would also help take water out of the container.
Ensure Pressure Levels Are Correct
RO systems should have pressure levels between 35 and 40 PSI. If your system’s pressure level is below that range, it could lead to inefficiency and more wastewater.
If yours does go below that level, here are some ways you can increase your water pressure:
- Adjust the pressure-reducing valve
- Adjust thermal expansion tank pressure (only for closed water systems)
- Install a booster pump
- Contact the local water supplier to check if there are pressure issues
Regularly Maintain Your System
Routine maintenance of your reverse osmosis system includes the following:
- Periodical cleaning or sanitizing (which may involve the use of hydrogen peroxide or sanitizing solution)
- Checking for wear and tear on components
- Replacement of filters and membranes
- Draining the RO storage tank (ideally done every night, or at the very least, every two weeks)
Here’s the recommended schedule for replacing filters and membranes:
|Six months to 1 year
The above-recommended replacement schedules aren’t set in stone.
For example, if your water source contains too many minerals, especially chlorine, you may have to replace the filters and membrane more often and much earlier than recommended.
Also, if the TDS of the permeate increases over time, take that as a sign to replace the membrane.
Install a Permeate Pump
There are reverse osmosis systems that come with a permeate pump pre-installed, which helps improve efficiency.
However, if yours didn’t, purchasing the pump separately and installing it later is still possible.
The primary use of a permeate pump is to reduce back pressure from the system’s storage tank, which allows the clean water to enter the tank more efficiently, i.e., less force is needed.
This allows the RO system to produce clean water (aka permeate) faster and more efficiently.
However, to reduce that back pressure, energy is needed. Instead of the usual electrical power, a permeate pump uses hydraulic or hydro energy.
Such is produced when the brine or wastewater enters its storage tank, which activates a piston. The piston allows clean water to enter its storage tank more efficiently and rapidly.
With a permeate pump installed, you can save as much as 85% of the waste or brine water. In other words, you can reduce the waste-to-clean water ratio to 1:1.
Use a Membrane Upgrade Kit
Most reverse osmosis systems come with multiple filters but only one RO membrane.
While that’s conventional, adding a second membrane to the system is a great way to increase efficiency. To add that additional membrane, you can use a membrane upgrade kit.
A second membrane does not just reduce the amount of wastewater. It also speeds up the water production process; thus, you won’t have to wait long for your system to provide clean, potable water.
Opt for an Automatic Shut-Off (ASO) Valve
An automatic shut-off (ASO) valve prevents water production when the storage tank is nearly full.
If the system is allowed to keep filling the storage tank until it is entirely full, more wastewater is produced; hence, you need a valve to stop it at the optimal time so no more brine water is produced.
There are three ways to get an ASO valve for your RO system:
- Pre-installed – some modern RSO systems have the valve up and ready for use.
- With the permeate pump – some permeate pumps come with an ASO valve. Installing both will significantly help in maximizing your system’s efficiency.
- Install separately – ASO valves are sold on their own, and you can have them installed on your RO system, whether with a permeate pump or none.
An ASO valve also helps extend the system’s lifetime by reducing wear and tear on the components. Like the permeate pump, it also doesn’t use electricity.
Choose an Efficient RO System
Old models of RO systems are known to waste vast amounts of water—even up to 20 gallons (76 liters) per one gallon (4 liters) of clean water they produce.
However, just like any technology, manufacturers of RO systems are constantly improving their designs to reduce waste water.
Thus, unlike before, you can pick a reverse osmosis system with a 1:2 or even 1:1 waste water to clean water ratio.
If you plan to purchase a reverse osmosis system, look out for a WaterSense label provided by the U.S. Environmental Protection Agency (EPA) only to units that meet specific standards.
The EPA announced in 2022 that it planned to have such labels for point-of-use RO systems. Hopefully, they will be implemented to significantly help future purchasers.
Pick an RO System That Recycles Water
Although most reverse osmosis systems on the market are more efficient, with 1:2 to 1:1 efficiency ratios, they still produce waste or brine water, whether one gallon (four liters), two gallons (eight liters), or 10 gallons (38 liters).
However, some manufacturers have developed zero-waste systems for those who want a unit that drains no wastewater.
In zero-waste RO systems, the brine or wastewater isn’t drained. Instead, it is returned to the plumbing system and routed specifically into the hot water system so you can use it in showers, dishwashers, and other purposes.
Speaking of hot water systems, you may want to check out our article, How To Install A Heat Pump Water Heater In 8 Easy Steps. Such knowledge may be helpful as you prepare your home for a zero-waste RO system.
Although we’ve mentioned reverse osmosis systems’ wastewater isn’t suitable for showers, in zero-waste systems, it is first filtered before being recycled. Thus, you can be sure that it’s safe.
You must also note that zero-waste RO systems are typically more complicated to install than the usual point-of-use system. Thus, consult an expert first before opting for this type.
Factors That Contribute to Wastewater in RO Systems
Now that you know how you can reduce wastewater from your reverse osmosis system, what brings about this wastewater?
The main contributing factors include:
- The recovery rate: This is the amount of purified water produced compared to the total water entering the RO system. A lower recovery rate results in higher wastewater generation. If the system is set to recover a higher percentage of water, more water will be directed to the drain as reject water.
- Feedwater quality: High levels of contaminants or impurities in the feedwater can lead to increased fouling and scaling on the RO membrane. This lowers the system’s efficiency.
- Membrane fouling and scaling: Fouling occurs when particles, microorganisms, or minerals accumulate on the surface of the RO membrane, reducing its effectiveness. Scaling and fouling increases the pressure required for water to pass through the membrane, leading to more water being sent to the drain as reject water.
- Operating pressure: The operating pressure of an RO system influences its efficiency. Although higher operating pressures lead to better water recovery, they increase energy consumption. Therefore, finding the optimal operating pressure is crucial to balancing water recovery and wastewater generation.
For those with traditional RO systems, reducing wastewater can be done by reusing the wastewater for other purposes (like watering plants), installing accessories (such as an ASO valve and permeate pump), or regularly maintaining the unit.
However, for those who are yet to get a reverse osmosis system or need to replace their old one, purchase energy-efficient models—those whose clean-to-waste water ratios are between 1, 1:1, 1:2, or 1:3.