Does Reverse Osmosis Waste Water? How Much Water Does Reverse Osmosis Waste?

Does Reverse Osmosis Waste Water? How Much Water Does RO Waste?

Does Reverse Osmosis Water Waste? How Much Water Does Reverse Osmosis Waste?

Reverse osmosis (RO) is a highly effective and popular type of water treatment. It is used for both residential and commercial water filtration. Reverse osmosis is great because it is easy to maintain, removes impurities, saves money, and produces exceptionally high water quality.  A drawback of conventional RO systems is that wastewater is a by-product of the reverse osmosis water purification process. Depending on the type, quality, and age of a system, they can use 3 – 25 gallons per 1 gallon of RO water produced.

“Wasted” can be a misleading term though which is why I prefer to reframe it as a reverse osmosis system uses water. Some RO systems do use way more water than they should – that’s wasteful! – if they are not properly maintained or are not a quality water purification unit. I don’t think any water should be wasted pointlessly.

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Does reverse osmosis waste water?

A reverse osmosis system uses more water than it produces. To produce 1 gallon of RO water, gallons of water are sent to the drain as wastewater, also called brine. It is just part of the purification process. From a conversation view, another drawback of reverse is that is does require energy (electricity) to operate.

In reverse osmosis, there is cross-flow filtration through the membrane. The permeate stream (product water) goes to the storage tank, and the waste stream with all the contaminants and dissolved inorganics goes to drain (also called concentrate stream or RO reject water).

So, yes, reverse osmosis produces wastewater unlike other water filtration processes. For example, with a standalone undersink carbon filter, all the water that goes in the system comes out of your faucet, minus the contaminants, and no waste stream is produced.

Some folks see the water usage as a significant disadvantage of reverse osmosis. Is reverse osmosis wasteful though? Another way to look at it is that there are other activities that “waste” all of the water used. For example, when you run the dishwasher or washing machine, or take a shower, 100% of that water is sent to drain. So arguably it’s a matter of perspective. 

As a whole, I don’t think a reverse osmosis filter is some evil, senseless method of water purification. In fact, I have a reverse osmosis system in my house because I have very hard water and I prefer the taste of reverse osmosis water.

There are two very important things when it comes to curbing reverse osmosis water usage

  • Before purchasing a water purification unit, thoroughly research it. Make sure it’s the latest, most efficient technology to cut down on unnecessary water wastage.
  • Proper system maintenance. Change your reverse osmosis membrane regularly! The older the membrane, the less efficient it is, and therefore the more water is sent to the drain.

The amount of water used by a reverse osmosis system is ultimately based on the RO system itself, age of the system, and water supply. For example, if the feed water is loaded with contaminants, it will cause the system to work harder and therefore the system will send more water to drain than in a location where the water supply is better.

Nowadays, there are water purification units that are designed to waste minimal to zero water (read more about these below).

Many RO manufacturers do not openly disclose their ratios probably because they can be high and it would probably scare customers away. If a manufacturer does not state the waste water ratio definitely ask about it before purchasing a system. The production ratio does depend on a variety of factors (as mentioned above) but a manufacturer should be able to provide a good estimate as to how many gallons of reject water there will be for every one gallon of RO water produced.

Membrane recovery rate impacts how much water a reverse osmosis systems uses. The recovery rate is how much water is being “recovered” as RO water. The higher the recovery rate, the less water that is being sent to the drain as reject water. However, some RO designs cannot handle high recovery rates – it leads to scaling and premature membrane fouling. So bear this in mind if the manufacturer is stating an exceptionally high recovery rate.

Most residential RO systems have an actual recovery rate of 10-25%, even if a manufacturer claims a reverse osmosis membrane has a 95% recovery rate. The recovery rate is what would be recovered if the incoming water is virtually perfect. Let’s face it: very few, if any of us, have perfect incoming feed water otherwise we probably wouldn’t be considering an RO to begin with.

This chart shows approximately how many gallons of water could flow to the drain per gallon of RO water produced under normal water conditions.

Amount of water sent to drain per one gallon of RO water produced

RO SystemBrand new system1 year old membrane2 year old membrane3 year old membrane
HydroGuard (HDGT-45)3 gallons5 gallons8 gallons10 - 25 gallons
Watts Premier (5SV)3 gallons5 gallons8 gallons10 - 25 gallons
Whirlpool (WHER25)3 gallons5 gallons8 gallons10 - 25 gallons
iSpring (RCC7)3 gallons5 gallons8 gallons10 - 25 gallons
Other ROs10 gallons10 - 20 gallons10 - 25 gallons10 - 25 gallons

You’ll notice that as a system ages, the more water flows to drain and is “wasted.” This comes down to the membrane. With usage (and time) the membrane is filling with more and more contaminants so in order to continue to produce pure water, the concentrate stream increases and more water is sent to drain.

A membrane should be replaced every two to three years. Once you replace the membrane, the efficiency improves and less water goes to drain. For example, if you replace the membrane in the HydroGuard system at year two, the waste water ratio would return to 3 gallons of water sent to drain per gallon of water.

What is Reverse Osmosis?

A reverse osmosis filter eliminates virtually everything in water including the majority of dissolved minerals and dissolved solids. RO systems separate pure water from contaminated water by removing ions, molecules, and particulates from drinking water. A reverse osmosis system improves the taste, odor, look, and overall safety of drinking water. A reverse osmosis membrane has a pore size of approximately 0.0001 micron.

Most reverse osmosis systems have the same basic components and work in a similar way, but the quality of their components can vary greatly. Make sure you are purchasing a quality system.

A quality reverse osmosis filter provides:

  • Safe, clean water. An RO system removes harmful contaminants such as metal ions, sodium, chloride, copper, chromium, and lead. Reverse osmosis may reduce arsenic, bacteria, fluoride, radium, sulfate, calcium, magnesium, potassium, nitrate, phosphorous, protozoa, and viruses.
  • High water quality (pure water) that tastes like bottled water. Most popular bottled water brands use reverse osmosis purification. Some folks prefer how reverse osmosis water tastes (or doesn’t taste, rather). RO water is pretty much “tasteless” since it is free from minerals, chemicals, and other organic and inorganic compounds. 
  • Financial savings. Stop buying bottled water! And forget a water filter pitcher or faucet filter- these are cheap temporary solutions that do not deliver purified water and end up costing way more than a reverse osmosis system in the long run.

Do Zero Waste Reverse Osmosis Systems Work?

Yes – they are still a RO system and produce wastewater, however it’s not flushed down the drain. They can be labeled as “zero waste” systems because the waste water is recycled. Most zero waste RO system return unused water from the system back to the home’s hot water supply. A drawback of this is that it means you are washing your hands, cooking, cleaning dishes, running the dishwasher, etc. with this wastewater, gross!

Best Reverse Osmosis System For Safe Drinking Water

Hydroguard HGDT-45 reverse osmosis systemEnjoy safe, clean water with the HydroGuard HDGT-45 series reverse osmosis system. This systems offers the filtration capabilities of a conventional 5 stage RO system, with the advantage of less filters to replace making it a more cost effective system. It reduces the levels of lead, nitrates, cysts (cryptosporidium, giardia), arsenic, sodium and more. This reverse osmosis system has a compact design, is easy to install, and uses sanitary quick change filters which makes changing water filters fast, convenient and sanitary. One of the revolutionary features of the HydroGuard HDGT-45 is its leak detector shut off valve (FLOWLOK ™) which silently guards against any water leaks which may occur. It also has a water pressure regulator to protect your system from water hammer and spikes in water pressure.

Ultrafiltration: Outstanding filtration process that produces zero wastewater, works smoothly at low water pressure, and no energy / electricity or tank required

Premiere zero waste ultrafiltration systemUltrafiltration (UF) is a powerful and effective water treatment technology. A UF membrane  filters out particulates like bacteria, viruses, protozoa, and organic / inorganic materials on a microscopic level. Ultrafiltration retains healthful minerals which are beneficial to health and taste (whereas RO strips them out). Read more about the differences between ultrafiltration and reverse osmosis here.

The Premiere PS-PURUF is a multi-stage drinking water system with a 0.02 micron ultrafiltration membrane plus two high performance 0.50 micron carbon filters. This system has over 99.9% bacteria and pathogen removal and it reduces heavy metals and chemicals including chlorine, chloramines, pharmaceuticals, pesticides, lead, VOCs, and more.

With ultrafiltration there is ZERO water waste. The PS-PURUF easily takes the place of outdated ultraviolet (UV) and reverse osmosis systems which can have significant waste water issues. Innovative technology lets you flush (clean) the membrane whenever it gets full of contaminants which provides substantial savings compared to other systems.

The PS-PURUF produces water on demand (up to 1.5 gallons per minute depending on your incoming water pressure) and no storage tank is required. This means no bacteria growth – tanks are notorious for bacteria growth – and significantly less space required. Ultrafiltration works smoothly in low pressure conditions.



A version of this article was posted in February 2020. I’ve changed and updated it with more information about reverse osmosis, the latest figures of how much water reverse osmosis uses, and the best RO systems for 2021.

How Much Water Does Reverse Osmosis Waste?
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How Much Water Does Reverse Osmosis Waste?
Reverse osmosis is a popular type of water filtration in America. It's great because it purifies really well, however conventional RO systems can send 3-25 gallons of water to drain ("wasted") per 1 gallon of RO water produced.
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