Clu In participates in the Amazon Associates affiliate program as well as other affiliate programs. If you make a purchase from a link on this site, we may earn a small commission at no extra cost to you. Thank you for your support!

Reverse Osmosis Waste Water Uses: 10 Ideas For Repurposing

In many situations, reverse osmosis systems are necessary for purifiying water, but reverse osmosis systems happen to waste a lot of water. Most reverse osmosis systems waste up to 3 gallons of water for every 1 gallon of water they purify. So what can you do? Here are 10 reverse osmosis waste water uses to reduce overall wastage.

The issue with RO waste water

The rejected water by RO has high TDS (Total Dissolved Solids) levels. These include inorganic salts and some organic salts. In addition to the salts there are a lot many metallic and non metallic compounds, which are eliminated from the tap water and gets accumulated in the water which the machines drains off.

These contaminants make this water undrinkable and unsafe not only for humans but for animals as well. And this is the reason most of the water directly gets drained and is overlooked.

However, these factors don’t make the rejected water unusable. Instead of wasting the rejected water, you can make some simple efforts and reuse reverse osmosis waste water.

Even the RO manufacturers have realised this problem and are working to design no water wastage or zero water wastage models. These machines have very high recovery rate where more than 50% of input water is recovered again and reprocessed second time to produce pure water from the waste water.

To further ensure that no water is wasted during, these models are designed with two separate tanks. One is for the storage of the purified water and the other tank stores the rejected water. The second tank can be connected to any other appliance in which this waste water can be utilised. But it is advisable that the water from the second tank should be diluted with some tap water.

Before we look some interesting life hacks to utilise RO waste water – remember one important common aspect for all its uses. The waste water is very high in minerals and salts and for its use it is always advisable to mix it with normal tap water so that the amount of mineral and salts gets balanced.

10 ways to reuse RO waste water

1. Use reverse osmosis waste water for Mopping and Cleaning Floors

Mopping floors every day is a necessity to keep the surfaces where you work of live free of dust, bacteria and infections. And a lot of water is utilised in mopping and cleaning surfaces. A rough estimation is that twice the drinking water in any family is utilised to clean and mop floors. You can use RO waste water for this very purpose in your houses and as well your work places.

But remember to mix the rejected RO water with some fresh water because firstly the soaps, detergents and acids will not mix properly in hard RO water and more importantly plain RO waste water will leave salt particles and other mineral particles on the floor, and can become a reason for corrosion of floor tiles and the tiles can lose shine if subjected to high mineral content water.

2. Use reverse osmosis Waste water to flush toilets

This is the best use for RO waste water.

Flushing toilets require a lot of water. An Ultra Low Flush toilet flushes at a maximum of 1.6 gallons (6 litres) per flush. This is ultra low flush toilet, so just imagine the quantity of water other toilets must be using for flushes.

Because of high water wastage in toilet flushes the Federal law currently mandates that all toilets manufactured in the U.S. must use an average of 1.6 gallons (6 litres) per flush or less.

So use the rejected RO water to flush toilets and simultaneously do your role in conserving water. The best thing you can do is directly connect your waste RO water pipe to the toilet flushing pipe. How clever it is to recycle a waste product to eliminate another waste product!

However when using the rejected water for cleaning for porcelain tiles and fixtures, check for any discolouration. In case you notice any discolouration, do not use additional acids to clean toilets because discolouration is an indication that RO waste water is doing its job superbly. You can use air-fresheners because this water will not help in cleaning the fragrance.

3. Use reverse osmosis Waste water to Wash your Car

According to a survey conducted recently approximately 14 litres or up to seven buckets of water may be wasted in day for car washing, and a lot of car owners wash their cars daily. It is estimated that a car requires wash every two weeks. (This does not apply to eastern countries). And if you are using fresh water or tap water for a car wash then you are wasting a lot of water, especially if you use a hose pipe because only half of the pipe’s waster is actually used in the wash and the other half is a complete waste. A 2016 report suggested that using a hose pipe for a car wash takes 75 litres! A better alternative than fresh water and to save all this waste is using the RO waste water.

Before you attach the RO waste water pipe to your car wash cleaning faucet, take note that do not use a scrub or brush if you are using hard water. Instead use a soft linen cloth, because the water itself will do the work of a brush. Secondly the force of the water should be minimal. The car should never be sprayed sharply with this kind of water.

4. Use reverse osmosis waste water to clean utensils

This again can be termed as one of the best utilities for RO waste water, primarily because washing utensils and cleaning sinks require a lot of water and secondly if they are cleaned with hard water they get cleaned better.

So the Waste RO water can be best used to wash off utensils sinks because salt content in it does not let left food get stick to utensils.

Use this water for rinsing the utensils and not for scrubbing. The salt environment will clean the utensils from all food and oily acidic particles. Then scrub the utensils with fresh low mineral tap water, as there is a chance that metallic utensils will lose their lustre and plastic utensils get coarse if scrubbed by hard water.

5. Use reverse osmosis waste water for laundry

Another excellent use of this water is to wash clothes because RO water is perfect with all the needed salt contents to take dirt away. In fact most of detergents made for washing clothes are rich in the salts and chemicals which are already available in RO water, especially sodium salts!

You can use this water for laundry; however avoid washing delicate fabrics as they may not react well with the TDS content and other metallic materials present in the rejected water.

6. Use reverse osmosis waste water to clean sewage pipes

The waste RO water can be used to clean sewage pipe at home or kitchen because of its saline nature. The pipes become greasy due to prolonged buttery and oily wastes. A little mixture of a dilute acid and RO water can do the required work. The waste RO water can also be used to remove the hard residual water which might have clogged in other appliances.

Now we will discuss some of the biological uses for RO waste water.

7. Use reverse osmosis waste water to Boil Eggs

You can also use the rejected RO water to boil eggs. This is a real smart and biological use. The water does not come in contact with the edible portion of the eggs, so no contaminants are ever going to be deposited on your food!

This is not limited just to boil eggs! Anything that has a casing and is not coming in contact with the edible portions can be warmed or heated using RO water. For example some people prefer eating fruits after heating them, so fruits having shells or hard skins like oranges can be heated in Luke warm RO water.

8. Use reverse osmosis waste water for Gardening

Before you use RO water for Gardening of plants please continue to read a little science.

RO rejected water can be used to water plants, in fact it is an ideal choice. But this is when the water you are receiving is low in TDS.

Most of the urban areas receive water that is low in TDS, so that makes it the apt choice for plant watering, as plants need mineral rich water. Most of the minerals which are in the water are essential for plant growth, and plants absorb them from the ground below.

But if the water has a high TDS or has carcinogenic metal compounds, then the same water becomes poison for the plants. The heavy metals will burn them.

So to be on the safer side, before using the water for your plants, ensure that the TDS level is not very high. Secondly mix the low TDS water with fresh tap water to balance out the mineral. And lastly check the quality of the water and its effect on each of your plants.

Water on each variety for a few days and measure its growth and general health. This will give you an understanding about which plants are responding better to hard water.

9. Use reverse osmosis waste water for Irrigation

Waste RO water can be used for irrigation, and you need to take all the cautious steps which we discussed in the Use RO waste water for Gardening point. Briefly, you need to use low TDS water and that too mixed with fresh water. You can examine the effect of this water on different crops, because certain crops grow well in hard water.

Remember – High TDS water should never be used for irrigation and not for gardening too as it has severe adverse effects on vegetables and or products which are eaten raw.

10. Can reverse osmosis waste water be used for bathing?

This is one of a hot topic and a lot of debate is available on this. Some support that one can bathe with the RO waste water after mixing some plain water as it gives you a saline touch.

Others completely reject the idea of hard water touching human skin.

Their argument is – RO “Reject” water is very high on hardness. RO removes hardness from your drinking water and concentrates it in the ‘reject’ water.

And high hardness can cause certain skin problems. Especially itching, skin redness and irritation in eyes can be commonly observed. Secondly it accelerates hair fall. And some argue that you don’t get the feeling of freshness if you use hard water as even the soap does not foam.

Scientifically many studies have been conducted on this topic and it has also produced mixed results. Some doctors actually suggest using specific bath salts for the betterment your skin. They say that like plants even human bodies absorb some minerals and salts via their skin.

Bathing or not remains every individual’s personal choice. If he or she feels that hard water suits his needs best then he can use RO waste water for this purpose by diluting it. It will save him from bath salts. And if the water is having an adverse effect then this stunt should never be tried.

Reusing, reprocessing and recycling reverse osmosis waste water

We already looked how we can reuse the contaminated water in local households, but the reality is that it does not make a huge difference in the conservation of the large volume of waste water.

Although RO remains as the best and most effective method for fresh drinking water, recent concern over RO waste water and its volume, has given rise to many studies and researches suggesting how to conserve and treat the discarded water from these essential household equipments.

Water treatment and purification is an old science and there are many effective ways that can come in use. Let us briefly look how some technologies can actually be very useful in the conservation process.


Evaporation is a time-tested methodology for reducing the water portion of water-based wastes. The evaporator converts the H2O from the water-based waste to vapour, while leaving the higher boiling contaminants behind.

If the RO waste water can be channelized properly and collected in large public reservoirs then this method can become very effective. RO waste water is not dirty water (in terms of quality), it’s just that its hardness/mineral content is different. So it is not wrong to feed it to a nearby rainwater harvesting system where evaporation does its work, specially in summers.

It will be beneficial to environment as the benefit of the evaporated water will again be yielded by the locality itself. The only requirement is that the waste RO water should not be drained into sewers as then this water becomes useless and evaporation can have no effect on it.

An important benefit of this method is that it requires low labour and hence becomes the most economic mode for the purpose. Secondly Evaporation technology can handle a much wider range of waste streams compared to membranes and traditional physical / chemical treatment methodologies.

The waste that remains can be further processed as the salts and other organic minerals can be used as fertilizers for plants and crops.

Mechanical Vapour Compression Evaporators and Thermal Evaporators have proven to be effective technologies for dewatering RO reject / RO concentrate waste streams.

Reusing the RO waste as the source water for a second RO machine

Another good possibility is to reuse the reject water from an RO system by feeding it directly into a 2nd RO unit. This way 20% of the water can be directly saved, as the second RO machine will again produce 20% fresh water from the supplied waste RO water.

However the likelihood of scaling of the 2nd RO unit increases as the water the 2nd RO machine receives has very high TDS and many contaminants. It becomes necessary that the 2nd machine should be pre-treated.

A Tubular Membrane Filter (TMF) system coupled with lime softening can reduce scaling and fouling of the 2nd RO machine and enhance its operation as well. The silver lining to this treatment technique is its recovery rate. Recovery rates increases many folds, and are around >95%! And lime softening ensures the health of the machine and no substantial reduction due to scaling is observed in the RO purifiers.

With the increasing cost of water and waste discharge, many companies are using this technique. It is an efficient and cost effective method for either retrofitting existing RO systems or for the incorporation of the process into newly designed systems. The reality is that some companies are actually doing business by setting up huge RO plants having Tubular Membrane Filter.

Desalination of RO Waste Water

RO is actually a method to desalinate the tap water, but it also open up a study as to whether the concentrate disposal of RO water can be further desalinated or not.

Desalination of unconventional water resources is becoming common as drinking water supplies are getting deteriorated. But desalination comes with a price because heavy cost and energy is required. If the costs are decreased then it becomes feasible to desalinate RO wastes. One of the approaches to make desalination cost effective is extraction of valuable commodities from RO wastes.

Although the extraction of various compounds like sodium, chlorine, potassium, and magnesium – from this kind of water is technically viable, profitability can be a concern considering the current market positions.

A study was conducted regarding the profitability issue, which suggested that the extraction of these commodities can yield good profit if the extraction is highly dependent on commodity pricing and final product purity, which can make Desalination a future technique for RO waste water conservation.


Electrodialysis is another method to conserve RO waste water. Experiments on this technique demonstrated to have an efficiency of over 80% reprocessing of the wastes, while using very small voltages. And using low voltages means low required energy which eventually means low costs. This method does not only reduce the waste volume but also provides additional feed for modern RO systems.


Globally we are experiencing acute water shortage and the future environmental conditions do not predict favourable conditions for water supplies. The amount of water available on Earth is also getting reduced due to global warming and other environmental hazards.

Conditions like these increases our responsibility and highlights that our approach towards the utilization of the water is a significant step for ours and for the future generation’s welfare. And wasting something in spite of having reuse alternatives is totally immoral.

RO waste water reuse, reprocessing and recycling is possible and the above mentioned activities are not unreal. It then becomes our duty as the citizens of mother Earth to make the most of whatever water Reverse Osmosis Water purifiers generate and use every drop of water efficiently.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.