What’s the reverse osmosis “waste water” argument?

A traditional reverse osmosis filtration system uses more water than it produces of RO water. To produce a gallon of purified water, multiple other gallons of water are sent down the drain as reverse osmosis waste water. This is just a fact of the purification process.

During the reverse osmosis process, there is cross-flow filtration through a membrane. The pure water (also called permeate stream or product water) goes to the water storage tank, and the waste stream (also called concentrate stream, RO reject water, or brine) that has all the contaminants and dissolved inorganics, goes down the drain. For a more detailed overview of how reverse osmosis works, jump to it here.

All other types of water filters – mechanical filters (i.e., sediment filters), absorption / adsorption (i.e., carbon filters), sequestration (i.e., scale inhibitor filters), and ion exchange – do not generate wastewater.  Essentially, all the fresh water that flows into these filters, flows out as treated water (minus the contaminants).

Reverse osmosis doesn’t waste water, it uses it

“Waste” 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 in fact use way more water than they should – that is wasteful! – if they are not properly maintained or are low quality systems. I do not believe any water should be wasted pointlessly.

The reverse osmosis debate is one of the most contentious water debates in America. RO naysayers say that water usage is a huge problem with reverse osmosis. However, this is misleading since there are other very common activities that “waste” water using this model.

Take hand washing for example. Hand washing is one of the best ways to protect yourself, your family, and those around you from getting sick. (Here’s when and how to wash your hands). When you wash your hands with soap and water, all the water goes down the drain. Is hand washing a wasteful and inefficient activity? From a water usage standpoint, yes. However, using water to wash your hands provides significant health advantages, just like drinking water safe does.

Similarly, showering, cleaning dishes, and washing clothes, all use water that is sent down the drain during the process yet there’s benefits to doing these activities of course. I do strongly believe in carrying out these activities with the environment in mind and doing them as efficiently as possible though.

I don’t think reverse osmosis is an environmental evil or senseless method of water purification. However, I think that everyone should determine if reverse osmosis is actually best suited for their water conditions or if they could accomplish their water goals with a different, more efficient technology. If you do opt for reverse osmosis, I also think consumers have the responsibility to do their research when purchasing a system to ensure it’s not unnecessarily wasteful, and to properly and regularly maintain their system which helps efficiency.

I personally have a reverse osmosis system in my house because my incoming water is very hard water (high TDS) and there’s traces of lead, chemicals, and other nasty contaminants. Plus, I like the taste of reverse osmosis water. Reverse osmosis provides me peace of mind that I’m protected from harmful stuff, and it lowers my TDS which I wouldn’t be able to accomplish with another filter.

How much water does an RO system use?

Generally, the reverse osmosis process takes 4 gallons of water to make one gallon of purified water. The amount of water used is based on the water supply and the RO system itself. Factors include contaminants present, amount of dissolved solids in the water, water temperature, membrane recovery ratio, condition of filters/membrane, size of the system, the pressure at which it operates, age of RO system, type of membrane that is used, and more. For example, if the feed water is loaded with lots of contaminants, the system has to work harder (and use more water) than if the water supply had less contaminants.

The chart above shows approximately how many gallons of reverse osmosis waste water per gallon of product water (average water conditions). You’ll notice that as a system ages, the more water used. This comes down to the membrane. With time and use, it fills with more contaminants, so the concentrate stream increases to keep producing pure water, and more water is ultimately sent down the drain.

There are water purification units designed to use minimal to no water (read more about these below).

What does the membrane recovery ratio mean?

Membrane recovery ratio is how much water is being “recovered” as RO water. It impacts how much water a RO system uses. The higher the recovery ratio, the less drain water. However, some RO designs cannot handle high recovery rates since it leads to membrane scaling and premature fouling. Keep 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 near perfect. Let’s face it: very few, if any of us, have perfect incoming feed water otherwise we probably wouldn’t need a reverse osmosis at all.

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 like listed above, but a manufacturer should be able to provide a good estimate of a waste water ratio.

How often should I replace my RO membrane?

The RO membrane is the workhorse of the system and should be replaced once every two to three years. If you have lots of contaminants in your water, you may need more frequent membrane replacements. Be sure to check with the manufacturer since not all membrane life is the same. A brand new membrane is at optimum efficiency 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 are zero waste reverse osmosis systems? Do they really have no waste water?

With all this talk about how much water reverse osmosis uses, it’s important to mention there are more eco-friendly options on the market. “Zero waste” might suggest it’s a different purification process in which no waste water is generated at all, but that’s not entirely true.  Zero waste RO systems have the same purification process and produce the same quality of water (ultrapure water). They do generate waste water, but it’s sent to be reused in your home so it doesn’t get sent down the drain. They are called “zero waste” because the water used (that doesn’t get made in RO water) is recycled making them 100% efficient technically. Most under sink zero waste RO systems send the reject water to your hot water supply.

A drawback of this water recycling is that you are washing your hands, cooking, cleaning dishes, running the washing machine and dishwasher, etc. with this reject water. So depending on what contaminants are in this recycled water, it can be disgusting to think about.

How does reverse osmosis work?

The basic idea behind reverse osmosis is to separate out the contaminants from the water molecules using a semi-permeable membrane. An RO membrane – which has a pore size of approximately 0.0001 micron – does this by removing ions, molecules, and particulates from drinking water.

This separation occurs in two steps: first, a pressure difference forces water through a semi-permeable membrane into an area where the concentration of dissolved solids is much higher than outside the membrane. Second, the concentrated solution passes back through the membrane, leaving purified water on the other side.

A reverse osmosis system eliminates virtually everything in water including the majority of dissolved solids and minerals. It improves the taste, odor, appearance, and overall safety of drinking water. In fact, reverse osmosis water is is pretty much “tasteless” since it is free from minerals, inorganic salts, chemicals, and other organic and inorganic compounds.

Tips for purchasing and maintaining a reverse osmosis system to use less water

Determine if you need a reverse osmosis system or if your filtration goals be achieved with other types of water filtration systems.

• Hard water / high TDS – only reverse osmosis will reduce and remove minerals and dissolved solids. If reducing TDS isn’t a priority or your TDS is less than 500 ppm, you may want to consider ultrafiltration or a carbon filtration system.
• Bacteria, viruses, cysts, pathogens – Although the pore size of an RO membrane is super, super small, other filtration types can still remove very small contaminants like bacteria, viruses, cysts, and pathogens. A 0.2 micron nanofiber filter or ultrafiltration (0.02 membrane) can tackle them.
• Chlorine – If removing and reducing chlorine is a goal, an activated carbon block filter will take care of this (no RO needed). If your water has a very high chlorine level, you may also want to consider an activated carbon block pre-filter because high chlorine may require more frequent membrane replacements.
• Retain healthful minerals – Reverse osmosis strips minerals so you’ll need to remineralize your water. Ultrafiltration,
• Dirt, sand, silt, sediment, rust  – A sediment filter will remove these larger particles. Available in a variety of micron ratings (1 micron, 5 micron, etc.) – the smaller the micron rating, the finer the particle a sediment filter will remove.
• Chemicals – Activated carbon filters can target chemicals. There’s different types of carbon (i.e., activated, activated catalytic, granular activated, etc.) and they’re not all created equal, possessing different effectiveness and capabilities for do make sure the specific carbon filter is suited for the chemical you’re trying to target.
• Heavy metals – Activated carbon filters can target heavy metals (dissolved and particulate). Like mentioned above, make sure the specific carbon filter is suited for the heavy metal you want to remove because carbon filters have different capabilities so check with the manufacturer.
• Before purchasing a water purification unit, thoroughly research it. Make sure it’s the latest, most efficient technology to cut down on unnecessary reverse osmosis waste water. Find out the recovery ratio and actual recovery rate. Also consider how frequently the water filters and membrane have to be replaced and factor that in.

Most reverse osmosis systems have the same basic components and work in a similar way, but the quality of their components can vary greatly. As they say, buy cheap, buy twice; and that’s especially true with RO systems and their replacement filters and membranes. There are high quality options out there that don’t cost much more than a rubbish ones, so go for the tried and tested. A quality reverse osmosis filter provides:

• • Safe, high quality of 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.
  • Low TDS. RO water is pretty much “tasteless” since it is free from minerals, chemicals, and other organic and inorganic compounds. Some folks prefer how reverse osmosis water tastes (or doesn’t taste, rather).
  • 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 money, effort, and time than a reverse osmosis system in the long run.
• Replace your reverse osmosis membrane and filters regularly. The older and more used the membrane, the less efficient it is (more water sent to the drain). Continuing to use a membrane or filter after its been used up is no good. A clogged filter or membrane can damage your system and it’s simply not as effective at removing harmful contaminants. You don’t “save money” by not replacing; you waste more water (costs money) and you don’t benefit from safe, clean water.

Best Reverse Osmosis System For Safe Drinking Water

Enjoy 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

Ultrafiltration (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 2022.