Does Reverse Osmosis Waste Water? Find Out Here!
Written by: Alexandra Uta // Last Updated: Aug 18, 2023
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A common concern among many prospective RO users is that reverse osmosis wastes water and might be unsustainable.
If you’re considering getting an RO system, you may want to know if that is true. Does reverse osmosis really waste water? How much?
This article discusses it all.
Contents
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Key Takeaways
- Reverse osmosis wastes water. It’s an important part of the RO purification process.
- Reverse osmosis wastes water as it separates the incoming water into two streams: One is called the permeate which is the purified water. The other stream is the brine which contains all the contaminants which need to be flushed down the drain.
Does Reverse Osmosis Waste Water?
So, does reverse osmosis waste water?
Yes, reverse osmosis wastes water. In fact, wasting water is an essential part of the reverse osmosis process, but more on this in a bit.
Do All RO Systems Waste Water?
Yes, all reverse osmosis systems waste water, including whole house and under sink RO systems.
How Much Water Is Being Wasted?
The amount of water a reverse osmosis system wastes depends on several factors.
- The first and most important factor is the feed water pressure at the RO membrane stage. The higher the pressure, the less water the RO system wastes. For this reason, RO systems with an inbuilt booster pump waste less water than those without a pump. For example, a standard under sink reverse osmosis filter system with no pump might waste 3-5 gallons of water for every filtered gallon it produces. On the other hand, a model with an internal pressure pump (like the AquaTru) might only waste about 0.25 gallons per gallon of filtered water.
- Also, if your pre-filters or RO membrane are clogged, you can expect to produce much more waste water.
- Other factors that influence the amount of RO waste water produced include the amount of contaminants in the water, feed water temperature, and membrane recovery rate and age.
Reverse Osmosis Waste Water Ratio
Reverse osmosis waste water ratio often comes up in discussions about reverse osmosis systems. The waste water ratio is the ratio of pure, filtered water to reject or waste water.
So, for instance, an RO system with a ratio of 1:5 will produce 5 gallons of waste water for every gallon of filtered water.
This ratio is closely related to another term “recovery rate”. A system with a recovery rate of 25% will be able to produce 25% pure filtrate. The standard recovery rate for under sink RO systems with no pumps is around 20%. As for systems with pumps, they have a recovery rate of at least 50%. That’s a wide margin and it’s clear proof that RO systems with pumps are better in that regard.
Why Does Reverse Osmosis Waste Water?
Reverse osmosis wastes water because the process is set to operate in a way that makes waste water production necessary.
Reverse osmosis filters water by forcing it through a semipermeable membrane under high pressure. The semipermeable membrane has tiny pores that stop contaminants from passing through it, leaving only clean water in the storage tank.
However, over time, the contaminants would start to build up on the membrane and could easily clog it. To prevent this, the RO system washes the membrane by continuously flushing it and moving the mixture of flushed water and contaminants into the drain (waste water).
How Can You Reduce Waste Water?
All reverse osmosis systems must produce waste water, but that doesn’t mean there’s nothing you can do about it. Below, we’ve explained four simple ways to reduce your RO waste water.
Optimize Feed Water Pressure
Feed water pressure is the pressure of the water entering the RO membrane housing to be filtered. A high feed water pressure means more water is forced through the membrane, and less water goes down the drain as waste water. If your RO pressure is too low, increasing it can help you reduce your waste water level.
Here’s how you can increase your feed water pressure:
- Add a booster pump to your RO system. A booster pump can reduce waste water production by up to 90+%.
- Add more pressure to home plumbing.
- If your system has a pressure valve, increase pressure at the valve.
Note: Reverse osmosis water pressure should be around 60 psi. Less than 40 psi will be problematic, and the same goes for way more than 60. So make sure you check your system’s pressure before adjusting it and also keep the pressure within the recommended range.
Recirculate and Repurify Reject Water
Another way to reduce your reverse osmosis waste water would be by recirculating it back into the RO system and repurifying it.
But his is usually only a thing in some whole house reverse osmosis system which use recirculation valves or multiple RO membranes installed in series.
Proper and Timely Maintenance of the RO System
A well-maintained RO system is less likely to produce excess waste water. But an old, poorly maintained system is a waste water bomb waiting to go off. So keeping your unit in good shape isn’t optional – it’s necessary to reduce waste water and ensure optimal performance.
You should replace your filters every 6-12 months and the membrane every 2-5 years.
Further Reading:
Use a Modern Reverse Osmosis System
Newer reverse osmosis models tend to waste less water and have higher recovery rates. They often come with features like inbuilt booster pumps that increase the system’s pressure and reduce the amount of waste water produced.
One such model is the AquaTru countertop reverse osmosis system which rejects a mere 20% of the feed water. This differs greatly from older models that only recover 20-30% of the feed water.
Do Zero-Waste RO Systems Work?
Zero-waste reverse osmosis systems are advertised as the final solution to the RO waste water problem. But do they really work? Granted, zero-waste systems reduce and even eliminate waste water, but there are some downsides that might make them not worth it.
To paint a clearer picture, there are two types of zero-waste systems on the market right now: The ones that reduce waste water by recirculating it back into the system repeatedly and the ones that reduce waste water by sending it down the hot water line.
Let’s look at both types and understand how they operate:
- Zero-waste RO systems that recirculate waste water: These systems repeatedly pass contaminated waste water back into the RO system to be filtered. The idea is to ensure that every drop of waste water is eventually restored into clean filtered water. However, the reality can be less than glamorous. In regular reverse osmosis filtration systems, the waste water is flushed out with the contaminants through the drain line. But with a recirculating zero-waste system, contaminants build up in the system, and the water to be filtered becomes more and more contaminated with each cycle. This increased and cumulative contaminant presence can wear down the filter elements, causing them to fold prematurely.
- Zero-waste systems that send contaminated water to the hot water line: The logic behind this is that instead of sending waste water down the drain, it should be redirected into the hot water line, where it can be used to wash hands or do dishes. However, this means you’ll be washing your hands with contaminated water (which may defeat the purpose of washing hands), and dishes may be discolored depending on the level of contamination. So while this method can eliminate waste water, it isn’t exactly hitch-free.
If you have any thoughts about the question, does RO waste water, please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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