How Much Water Does an RO Purifier Waste?

Q: How much water is wasted to fill a 20 L can?

Normally, filling a normal 20-liter can with water from the purifier will lead to wastage of between forty and sixty liters.

Q: Is RO wastewater good for plants?

It is only applicable to crops that can handle high levels of salt. In case you have to apply it continuously, this may lead to the death of those sensitive ones. Just be sure to dilute using plain fresh water if you want to use it anyway.

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How much water does an RO purifier waste? This is a matter of concern for all those people in India who are trying to be kinder to the environment. Although we understand the importance of pure drinking water, the question is—at what price? In most cases, for residents in some cities of India, the sight of gallons being poured down the drain feels painful. What we refer to as “reject water” or “wastewater.” Although Reverse Osmosis (RO) remains the most effective technology to soften hard water, it comes with a drawback, i.e., waste. However, it raises the question: how many liters exactly pass as waste? Can one prevent such wastages of RO purified water?

What’s the ratio of water wastage in RO?

First let us clarify some figures. In the past, most machines had very bad ratios. In those days, one liter of pure water translated into three wasted liters from any RO system; hence, the 3:1 ratio.

Nonetheless, technology is better nowadays.

The ones in use today are improved and of higher efficiency. They usually come with ratios of the type 2:1. So you lose two liters for every one liter of drinking water.

This is how it goes mathematically.

Assuming your family consumes approximately ten liters of water daily (inclusive of cooking water):

Old RO: You waste 30 liters.

Modern RO: You waste 20 liters.

This amounts to almost six hundred to nine hundred liters of water being wasted every month. The volume is so large that it can fill up even the biggest tankers. This is technically called the recovery rate, which most Indian buyers do not know about.

Why Does an RO Purifier Waste So Much Water?

1. The Flushing Mechanism

Imagine that the RO membrane is a very small mesh or sieve. This machine requires high pressure to drive water through such a small hole so as to remove dissolved salts and heavy metals. However, to prevent blocking of this mesh by solid particulate matter present in water, the apparatus has a self-cleaning unit that washes away automatically.

This is possible only through forcing it to flow out into the drain, carrying all the impurities and chemicals, including highly concentrated salts. The concentrated form of this kind of water is referred to as “reject water.” Failure to expel this kind of dirty water would lead to choking of the membrane, hence stopping the engine.

2. The Role of TDS (Total Dissolved Solids)

The quality of your input water determines how much waste there is to be produced. In case you are using high TDS water like borewell water, then it has more work for RO, and a larger flushing of water is required for reducing the TDS level to a safe range. Lower input TDS leads to reduced wastage.

Government Regulations on RO Wastage in India

The fact that the government intervened here is very important for those who wish to purchase water purifiers.

1. BIS (Bureau of Indian Standards) Norms

Very strict regulations were imposed by BIS. For any new water purifier that is seeking after the ISI mark, it has to comply with some particular efficacy standards as demanded by the law. According to this rule, the maximum wastewater allowed should not exceed 60% of the total input. It means then that the recovery ratio should be a minimum of forty percent, forcing better manufacturing of high recovery purifiers.

2. NGT (National Green Tribunal) Guidelines

The NGT went even further. They made a decree prohibiting the utilization of RO purifiers in places having a TDS level less than 500 mg/l. Why? Because use of RO in such low TDS level soft water leads to avoidable water wastage and does not accrue any hygiene immunity benefits whatsoever.

7 Clever Ways to Use and Save RO Waste Water

In a standard machine, it is impossible to completely prevent the waste, although in such cases one may recycle the RO wastewater to cut costs and conserve nature.

Is it possible to drink RO wastewater?

No! Don’t drink. After going through the filter, it contains too many salts and impurities that have been left behind by the filter.

Here is how you should use it:

Washing Utensils: Washing utensils is a very good way of using this reject water rich in salt that enables soap to form lather easily.
Mopping Floors: Just like with tap water, mopping your house with a bucket of reject water will do the job perfectly.
Flushing Toilets: It saves most of all. Connect the outlet of the reject water treatment unit to your WC flushing cistern. With this, you will be eliminating the need for clean water for flushing purposes.
Car Washing: In case you decide on washing your car using home-based approaches, this is the kind of water to employ. It is harmless to the polish.
Watering Plants (With Caution): You can use it for hardy plants. But don’t put it onto sensitive plants too often since the high amounts of salt may be harmful if used repeatedly.
Pre-Washing Veggies: Prior to giving them a final rinse with clean water, make use of it in washing away mud from potatoes and carrots.
Laundry: For scrubbing collars and socks in separate buckets, apply reject water if available.

Technologies to Reduce RO Water Wastage

New water purifier buyers should also consider these options to reduce RO water wastage.

1. Zero Waste RO Purifiers

These are machines that return the reject water into your overhead storage tank, and they are commonly referred to as “no drain” or “zero wastage” purifiers. Caution: This increases the TDS level of the water in your tank over time. Make sure the TDS level of water in your tank is at a safe limit.

2. Permeate Pumps

You can add a permeate pump to your current RO. It lowers the amount of pressure needed for filtering. This can make things work better and save up to 50–80% of water.

RO vs UV vs UF: Which Wastes the Most Water?

One should know that only RO technology wastes water.

RO: Too much waste (essential for taking off salt).
UV Water Purifier: No wastage. It kills bacteria only.
UF Water Purifier: No wastage. It strains muddiness.

In cities having municipal water with TDS being low (<500 ppm), skip RO if possible. A combination of UV and UF filters provides you with zero-wastage safe drinking water.

Conclusions

An RO water purifier is important, but all hope is not lost on water wastage. By considering the recovery percentage and adhering to the NGT instructions, one can decide wisely. If your TDS level is high, then you have no option other than using RO. Ensure that you use the rejected water for either mopping or gardening. In case your tap water is already soft, change over to a UV or UF unit. Let us keep on treating our waters without any harm to the environment.

Frequently Asked Questions (FAQs)

How much water is wasted to fill a 20 L can?

Normally, filling a normal 20-liter can with water from the purifier will lead to wastage of between forty and sixty liters.

Is RO wastewater good for plants?

It is only applicable to crops that can handle high levels of salt. In case you have to apply it continuously, this may lead to the death of those sensitive ones. Just be sure to dilute using plain fresh water if you want to use it anyway.