Why Reverse Osmosis Waste Water & How to Reduce It

Reverse osmosis (RO) systems are incredibly effective at removing contaminants from water. However, some people are reluctant to use them as they’ve heard they produce a lot of wastewater. While this is true, there's a good reason for this.

In this guide, we'll take a look at why RO systems waste water, how much they waste, and best practices to reduce waste water.

Why is Water Wasted in Reverse Osmosis?

In a nutshell, reverse osmosis “wastes” water because the filtered contaminants needs to be flushed away. 

During cross-flow filtration, water filters through a membrane which is where all the contaminants are collected. Then, those contaminants get washed away during a process called regeneration, where a large volume of water is used to flush the system.

That said, “wastewater” can be a misleading term in the case of reverse osmosis. To be clear, there’s no question that a poorly maintained or low-efficiency reverse osmosis system can waste a lot of water. However, that’s a product of a poorly designed system, not the RO process itself.

Look at it this way; when you wash dirt from your hands, you’re not wasting water just because it’s going down the drain. It’s simply a part of the cleaning process. In order to get your hands clean, you’ll have to “waste” some water.

Reverse osmosis removes contaminants from water, just like washing hands takes away dirt and germs. A well-designed RO system will use as little water as possible to do this. Unfortunately, there’s no way to completely avoid water washing away because that’s simply how the process works.

How Much Water Does Reverse Osmosis Waste?

The average reverse osmosis waste water ratio is 4:1. This means for every gallon of clean water, the RO system produces 4 gallons of wastewater.

That said, a well-designed reverse osmosis system will waste very minimal water. Fortunately, as RO systems become more advanced, you’ll find more and more options for systems that use significantly less water.

How to Reduce Waste Water In an RO System

There are several ways to reduce the volume of wastewater an RO system produces or to make use of the wastewater, so let’s see what they are.

1. Save Your Water

Although this won’t reduce the volume of wastewater your system produces, it allows you to reuse the water so that it isn’t simply wasted.

First, extend the reverse osmosis pipe so it deposits wastewater into a tank outside your kitchen. Then, you can use that water for other household things. For example, you can use RO wastewater to:

• Wash your car
• Water your garden or plants
• Mop your floor
• Wash your patio furniture
• Rinse paint brushes
• Clean off muddy shoes

Unfortunately, RO waste water is not ideal for bathing yourself or your pets. But you can still use it for anything that doesn’t require clean, potable water.

2. Recycle Your Water

Some RO systems will recycle water for you, eliminating the need for a water tank. Instead of discharging the water down the drain, they simply recirculate any discharge water back through the system.

The main thing to remember about this option is that contaminants may build up in the water that recirculates, which may eventually damage the RO membranes. Still, it’s an excellent way to reduce the amount of wastewater the system creates, and the best thing is that you don’t even have to do anything. 

3. Maintain Your System

As with any system, an RO system needs proper maintenance to function. You’ll need to regularly replace the RO membrane to ensure as much water is getting through as possible. If the membrane is damaged or clogged, less water is filtered and more water passes through as rejected water (wastewater). 

So, it’s vital to regularly clean and replace the membranes in your system. Depending on the model and usage, expect to change filters every 6months – 1 year for a standard system.

4. Increase Your Water Pressure

The water pressure level directly affects how much water an RO system uses. The ideal water pressure for a reverse osmosis system is 35-40 PSI. Any less than that, and you would waste quite a lot of water. Giving your pressure a bit of a boost can help maximize your system’s efficiency and, as a result, reduce the amount of water that’s wasted.

RO Systems With The Best Waste Water Ratio

If you’re curious about which RO systems use or waste the least amount of water, we’ve listed a few options below. However, for a more comprehensive list of systems with the best overall performance, refer to our article on reverse osmosis system reviews.

• NU Aqua Efficiency Series: The NU Aqua Efficiency RO system offers a 2:1 wastewater ratio, which means for every 1 gallon of wastewater, you’ll get two gallons of pure water. This makes it twice as efficient as most of the other systems mentioned in this article.
• Frizzlife PD600 Reverse Osmosis System: The Frizzlife PD600 has a wastewater ratio of 1.5:1. That is incredibly efficient compared to standard RO systems. It means that 1.5 gallons of clean water is produced for every gallon of wastewater. 
• Waterdrop G3: The Waterdrop G3 boasts a wastewater ratio of 1:1. In other words, it only uses one gallon of wastewater for each clean gallon it produces. It also has a 400 GPD flow rate and a 7-stage filtration process that can remove more than 1,000 contaminants from water. 
• iSpring PH100 Under Sink Reverse Osmosis System: The iSpring PH100 Under Sink system is a high-efficiency RO system with a 1:1 wastewater ratio. It removes more than 1,000 different contaminants, including up to 98% of lead. It also has a ⅜” fast flow line that increases water flow through the membranes.