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How Much Water is Wasted During Reverse Osmosis?


I t’s no secret that tap water is not the cleanest water for drinking, which justifies the development of many systems designed to filtrate the impurities in the drinking water. One of these systems is called reverse osmosis and is a very popular one, too. However, there is one concern related to installing one, and that would be the percentage of water waste. While it’s a fact, this detail can often be misleading, as it requires deep analysis to discover how bad this drawback really is. We will try to put this as clear as we can, so you can make an unbiased decision regarding the purchase of a RO water purifying system.

The basics of reverse osmosis

This is not a regular water filter, it’s a more complex system that uses a very fine membrane, with a porosity of approximately 0.0001 microns. As the water is passed through this membrane, ions, molecules, and particles of impurities are removed. The purpose is to improve the quality of the drinking water by eliminated unpleasant odors, dangerous contaminants, and dust or rust particles that alter its aspect.

While most systems do the same thing, their efficiency lies in the quality of the components, so you should purchase a top-quality model that will bring many welfares in the long run:

  • Healthy water
  • Simple upkeep
  • Money savings

The biggest drawback of this water filter is that it uses many gallons of water to produce one gallon of clean water. To be more precise, it wastes 4 gallons of water for each gallon of purified water. The resulted water is sent to the drain unless you store it for later use. Compared to other filtration systems that return all the filtered water as clean water, this one is the most wasteful. Therefore, its utility comes to question.

However, reverse osmosis is not entirely bad, as it’s highly efficient in providing purified water without the use of any electricity, which limits the expenses and the effects on nature. From the same point of view, you might state that the dishwasher or the washing machine is 100% wasteful as all the water they use is eventually sent down the drain. And yet, you still own and use one.

Actually, the water is not literally “wasted”, it’s just that these systems require a high water pressure, so a high amount of water is run through the membrane to deliver a shorter amount of purified water. In other words, it’s similar to showering at a high water pressure; some of the water will get on your body and clean and, and another part will run beside you and go down the drain.

The amount of water used by a reverse osmosis system is ultimately based on the RO system itself, the age of the system, and what is in the incoming water.

How can you minimize waste?

1. Recycle discharged water

You can find other purposes for the discharged water, so you will somehow manage to reduce the waste. Recirculating it through the reverse osmosis system is not a good idea, because the number of impurities and scale could damage it. Therefore, you will have to find better ways to do that, and you will discover them further below.

2. Check the water pressure

If your water pressure is not high enough, more water might be wasted as it is sent through the RO membrane. Therefore, make sure the pressure at the tap is over 40 PSI, otherwise, it will contribute to the waste percentage. Check the pressure reducing valve or get in touch with the local authorities to detect the issue.

3. Perform regular upkeep

After installing this filter in your house, you will have to keep a constant eye on it. Usually, a complex system has up to 5 different cartridges, including the membrane. Each has a certain lifespan that is influenced by the overall quality of the tap water and the intensity of its use. As such, you must check the cartridges every once in a while and make sure they perform properly and don’t need a replacement. If you take good care of the filter, it will last for as long as 15 years and the water wasted will be significantly reduced.

Smart ways to reuse that wasted water

The opinions in this matter are split; some say that the rejected water can’t be reused because it contains high amounts of TDS or total dissolved solids, which make the water impossible for drinking. Moreover, the salt levels are high and it contains organic matter, so it’s not recommended for cleaning objects around the house because of limescale deposits. If you can’t fix the water waste issue, the least you can do is minimize its impact. Therefore, you can find some ingenious ways to repurpose the resulting water so that the damage will be minimal.

  • House chores
    Although the salt and deposit levels are high, the water can be used for some household chores like mopping, pre-rinsing the laundry, or washing the dishes. You shouldn’t use the water for appliances like the washing machine, the iron, or the steam mop because it might cause scaling.
  • Car wash
    You can have fun while washing your car using the wasted water coming from the RO filter instead of consuming more water. It takes around 20 liters of water to clean a car, so the saving will be considerable.
  • Toilet flushing
    One flush requires around 6 liters of water, do the math, and see how much water you send down the drain in one day. You can reduce the waste by using the water resulted after filtering tap water, considering it is already destined to be wasted.


Yes, reverse osmosis filtration systems indeed waste water along the water-purifying process. As a disclaimer, so do other appliances in your house, so we can state that this side effect is somehow inevitable. On the bright side, there are ways to reduce the waste to a minimum, as long as you pay attention to the functioning of your system. With the proper upkeep and some ingenious hacks, you will manage to get the most of your RO purifying system and overcome the downside of the discarded water.

Tobey Hunter
Tobey Hunter
Tobey is the editor-in-chief at P2Rx™, his experience both in the field of journalism and a keen interest in the topic of pollution, a subject he previously covered in his career in multiple pieces, making him the expert of our team. What Tobey learned from his background is that researching each topic thoroughly is the only guarantee that an article will depict a truthful picture, a policy that he strictly follows. In his off time, he indulges in reading modern literature and binging on the latest TV shows.