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Production and Treatment of Waste Water in Reverse Osmosis Systems

by Dr. Jonathan Doyle - Updated September 27, 2021
The increasing demand for reverse osmosis water systems is not surprising, considering how advanced this water filtration technology is. Here is a blog that we wrote before that explains how powerful the reverse osmosis is: How Does a Reverse Osmosis Filter System Work? RO system efficiently removes contaminants, providing high-water, clean, and healthy water for drinking and cooking. However, it also produces wastewater – a major concern for users. Traditional reverse osmosis systems produce up to four cups of wastewater for every cup of filtered water.
How is this possible?

Reverse Osmosis Waste Water

A reverse osmosis system uses more feed water and produces less filtered water. Let’s discuss the working principle of reverse osmosis to establish this fact. 
Reverse osmosis involves forcing water through multiple extremely-fined membranes, thanks to the composition of water. The RO membrane prevents harmful substances like heavy metals, sediments, viruses, bacteria, and others from passing. 
The water that goes through the RO membrane contains no contaminant. However, the concentrated water on the other side of the membrane is the "wastewater," containing all the removed impurities. It is eventually flushed out. 

How much wastewater does the reverse osmosis system produce?

This depends on the water pressure of the system. The traditional reverse osmosis water filter systems use up about four gallons of wastewater for every gallon of filtered water produced. This is due to the presence of a water tank and the resulting low pressure of 7-8 psi. The ideal pressure is within 35-40 psi.
However, with advanced technologies emerging, the reverse osmosis filtration process is now more efficient. The modern reverse osmosis systems do not have tanks. Instead, they are equipped with powerful internal pumps for increasing the water pressure.
You can only get 75 gallons of pure water daily out of a traditional RO system because of the low pressure. In contrast, you can get up to 800 gallons of filtered water out of the advanced tankless models. The latter is also more efficient, with a waste ratio of 1:1 or 2:1, translating to 2 gallons of pure water for every gallon of wastewater.
The Waterdrop G2P600 is popular among other reverse osmosis systems because of its 600 GDP large water capacity. It uses up only a cup of wastewater for every two cups of pure water it dispenses. Unlike the traditional RO water purifiers with tanks, this model is tankless and can help you save up to 600% more water.
The condition of the filter also contributes considerably to the overall efficiency of the system. If the valves are worn out, your system will most likely produce more wastewater. A consistent maintenance culture can solve this problem.

Reducing Waste Water

The simple solution is to improve the drain ratio from the two aspects identified above.

Maintain an adequate water pressure level

The reverse osmosis system will produce more wastewater at lower water pressure. Therefore, running at a household water pressure lower than the ideal 35-40 psi range can be counterproductive. If your pressure valve is okay and you are still running at low pressure, kindly check with your local water authority for possible pressure issues.

Maintain your water filter properly

The only way to get the best out of reverse osmosis filters is to check on them regularly. Most reverse osmosis water filter systems come with a five-stage filter cartridge setup. The filter in each stage is different and made specifically for a group of contaminants. Thus, the service life of each filter is different. The average service life of a reverse osmosis filter is between a year and two years, but it may be shorter or longer.
It is best to replace your filter once it expires. This, alongside other maintenance activities, can ensure you get the best filtration results and higher efficiency.
Learn more about how to maintain your water filter through Tips for Maintaining Your Home Water Filtration System.

Getting The Best Out Of Wastewater

Wastewater from reverse osmosis water is not suitable for drinking or cooking. However, you can store it in a large tank outdoors and recycle it for any of the following applications:

Washing of cars

Washing a car requires about 14-75 liters of water per session. The accumulated wastewater from your reverse osmosis system can easily meet this need. 

Household activities

Mopping the floor is another good use of wastewater. Again, the effect is similar to using tap water – using wastewater even reduces possible salt deposits and stains. 

Flushing of toilets

While you cannot use the wastewater for bathing or laundry because of the hardness of the water, you can use it to flush your toilets after use. It is also suitable for cleaning up your bathroom fixtures and faucets. 
We have a detailed blog that introduces several ways to reuse your RO waste water, check this out: Is the "Wastewater" Produced by the RO System Really Wasteful?

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