Richard Arconti 
Reverse osmosis water filters provide crisp, refreshing, and safe water. They safeguard our tap water from chlorine, fluoride, bacteria, inorganic matter, heavy metals, and viruses that threaten our health. However, one of the biggest knocks against reverse osmosis systems as a water treatment solution is that they “waste too much water!”
But is that true? In this article, we will review if reverse osmosis does indeed waste water, and if RO systems are worthwhile filtration options considering the facts.
Does Reverse Osmosis Waste Water?
As you will see in this article, the claim that reverse osmosis wastes water is not completely wrong but has become a bit of a misnomer through the years. Especially as technology has advanced to create much more efficient RO options.
Every water filtration system goes about purifying your water in slightly different methods. In the case of reverse osmosis, extra water is required to cleanse the filters of the harmful contaminants it removes from your tap water, leading to additional water being used.
The additional water required varies widely based on the type of reverse osmosis filtration system being used. Later in this article, we will discuss the most efficient RO systems, and ways to not only reduce RO waste water but also ways you can reuse the waste water so it gets put to good use.
How Much Water Does Reverse Osmosis Waste?
The average reverse osmosis system will use approximately 4 gallons of water for every 1 gallon of filtered water created.
That said, different reverse osmosis systems offer different waste water ratios, which we cover below. In the overall picture of household water use, reverse osmosis waste is pretty insignificant. A good way to think about it is like the water used to wash your hands. It’s not too much, and isn’t necessarily “waste”.
There are many factors that go into how much water your RO system will use. Perhaps the one with the biggest impact is water pressure. Homes with water pressure below 40 psi may experience less efficient water usage.
Another important factor is your home’s water composition. Is your water very harsh with many contaminants? Do you have well water? This makes maintenance critical so that filter and valve wear and tear don’t lead to higher water discharge.
Reverse Osmosis Waste Water Ratio (Efficiency Ratio)
The typical reverse osmosis waste water ratio is 4:1. This means for every one gallon of filtered water, a RO system will waste approximately 4 gallons of water.
You may see a lot of low-cost options that claim they have a 1:1 ratio. The truth is that the actual ratio is pre-determined by the membrane supplier. Your specific waste ratio will depend on factors like water quality, water pressure, pH levels, and more.
That said, if you want a lower waste water ratio, you absolutely can. It will just come at the expense of your filter life. Because the “waste” water is required to cleanse your filter membrane and allow it to last a reasonable lifespan, a low ratio will mean a shorter filter replacement cycle.
But there is good news! Reverse osmosis systems have continued to evolve with more efficient options on the market. Tankless reverse osmosis systems have become popular due to their water efficient design.
There are indeed residential tankless RO systems with true 2:1, 1:1, and even 1:2 waste water ratios. High-efficiency tankless reverse osmosis systems are capable of delivering 2 gallons of filtered water with just one gallon of waste.
Why Does Reverse Osmosis Waste Water?
Reverse osmosis systems work by pushing your tap water through an RO membrane with high amounts of pressure so that the only thing to make it through is pure H2O.
In order to do this, the filter membrane requires consistent flushing to remove the harmful contaminants it removes. Reverse osmosis membranes have pores that are only 0.0001 micron, so they get clogged very easily if not flushed.
If the filters are not cleansed on a consistent basis, it will lead to damaged filters, lower performance levels of your system, and more frequent filter replacements. While membrane flushing may seem redundant or wasteful, this is the price required for high-purity fresh tasting water.
Can I Reuse Waste Water From Reverse Osmosis System?
Reverse osmosis wastewater does have other uses for both your home or office.
Before we get into how RO wastewater can be reused, it is important to clarify that waste water from any source should not be used if the TDS or contamination levels are too high. It would be prudent to test the RO waste water before reusing it to ensure it is ok. Some tankless reverse osmosis systems even come with TDS displays built in.
Now that we have that short disclaimer out of the way, here are some great ways RO waste water can be reused:
Water Your Plants or Garden
If you enjoy gardening or have house plants, reusing RO waste water can be an efficient way to water your greens. Especially if you live in a city where TDS levels tend to be lower. We advise you to ease into it and slowly try the RO water on a variety of plants to see how they react over time.
Wash Your Car
The use of RO wastewater is perfect for washing cars. The water won’t harm your car’s paint and is just as good as normal hose water. There is no need to waste drinkable water from your hose if you have perfectly good RO water to reuse! Depending on your water, the only downside might be water spots if you have very hard water.
Household Chores
For floors, utensils, and bathrooms, reusing your RO waste water is an excellent alternative to using precious potable water for household cleaning. You can store some waste water for later use around the house.
This is a great solution if your floor has a lot of foot traffic, you will go through a lot of water moping floors. You can even flush toilet water and clean your faucet and fixtures with reused water. If you are using waste water on porcelain, be careful to test it first to make sure it will not lead to discoloration.
Pre-Rinse Laundry
RO waste water can be used to pre-treat your clothes when it’s time for laundry. If you have stains or want to soak your clothes before a load of laundry, reusing the RO waste water can come in handy. But it is worth noting if your water has very high TDS it can be hard on the clothes fabric.
How To Reduce Reverse Osmosis Waste Water?
There are several options to minimize the amount of water your reverse osmosis system discharges. In this section, we will go over things you can do to get the most efficient RO filtration possible.
Use An Efficient System
Modern reverse osmosis systems are becoming more efficient as technology evolves. When looking for the best reverse osmosis system, identify which options have the best waste water ratio. Some systems even come with recirculation to use the discharged water in the filtration process.
High-efficiency tankless reverse osmosis systems, for example, can have a waste water ratio that is multiples better than some traditional tank-based ROs.
Water Pressure
Most reverse osmosis systems work best with water pressure above approximately 35 PSI. If your home does not have adequate pressure, your RO system will still function, just not optimally.
If that is the case, there are some reverse osmosis systems that come with an integrated booster pump so you won’t have an issue. Separately, you can also purchase a small booster pump for your RO. They are relatively cheap and easy to install.
Perform Regular Maintenance
Having a damaged RO membrane filter or valve can significantly impair not only the efficiency of your RO system but also the purification quality. An RO membrane filter should last up to 2 years if maintained properly.
Other included filters like sediment filters, mineralization filters, and carbon filters may last for 6 months to a year. Knowing your system’s maintenance requirements will ensure your system will last for years to come while conserving the most water possible.
Reuse Your RO Waste Water
As we discuss above, there are several options for how you can reuse your reverse osmosis waste water. And if you are able to reuse the water discharged from your system, is it really wasted?
There are other options to recycle the waste water like feeding it to a hot water faucet line or another fixture where you don’t require pure water.
Is Reverse Osmosis Worth The Cost?
Every water filtration solution will have its benefits and drawbacks. As we have seen, RO systems do use additional water to cleanse the filtration system of harmful contaminants, but is it fair to classify them as “wasteful”?
To summarize if a reverse osmosis water filter system is worth it, let’s break down the numbers. According to the EPA, one gallon of tap water costs on average $0.00295. Now if you say an RO of average efficiency (not high efficiency) has a waste water ratio of 4:1, it would cost approximately $0.015 cents for one gallon of filtered water.
If bottled water is the most used alternative, one gallon of wholesale bottled water costs $1.17 according to IBWA. If each person drinks a little less than a gallon of tap water per day, a family of four would consume about 3 gallons per day, not including tap water used for cooking or any other uses.
Putting it all together, a year of bottled water would cost $1,281 vs RO filtered water would cost $16. Even after adding the cost of the RO system itself and any replacement filters, you come out far ahead. And that’s not to mention that RO water is likely better quality than the bottled water!
These are rough numbers for illustrative purposes, but directionally they get the point across that reverse osmosis systems are by far worth it. Not only in terms of money but also in terms of reducing plastic use.
Frequently Asked Questions
Can you cook with reverse osmosis waste water?
No, you should not cook with reverse osmosis waste water because it is high in TDS and other contaminants.
How do you collect reverse osmosis waste water?
The simplest method of collecting and storing the waste water would be to extend the waste water outlet line from the RO into a holding tank or bucket. The water that is collected can then be stored and used for later use.
Can you use reverse osmosis water for showers or baths?
No, it is not advisable to use reverse osmosis system waste water for bathing because the discharged water will be concentrated with impurities you will not want covering your skin.
