Reverse Osmosis Wastewater FAQs

Every reverse osmosis system creates wastewater during the purification process. This is because the membrane has a very small pore size of 0.001 micron, and as the RO membrane removes contaminants from the water, it requires additional water to rinse the membrane to prevent it from loading too quickly. This water, also known as the concentrate stream, RO reject water, or brine water, is then usually sent to the drain saddle.

The average system has a ratio of 1:4. This means that for every 1 gallon of pure, filtered water, about 4 gallons of water is sent down the drain as wastewater. However, this number can vary depending upon a number of factors, resulting in anywhere from 3 gallons of wastewater to as much as 25 gallons of wastewater per 1 gallon of purified water.

Because of the wastewater produced, it is mindful to consider whether or not you really require a RO system for your home, or if another less wasteful system would be adequate for your filtration needs. However, using a RO system is not as bad as it sounds when put into perspective. The average 1:4 ratio gives RO a 25% efficiency rating, but when you wash your hands, run the dishwasher or clothes washer, or take a shower 100% of the water is “wasted” and sent down the drain. Plus, a good RO system creates pure, high quality water for less money than bottled water with low maintenance requirements.

There are a few steps you can take to reduce the amount of wastewater your RO system produces. Some factors that affect the amount of wastewater are out of your control, such as the temperature of the water (lower temperatures result in higher amounts of wastewater) and the amount of TDS and other contaminants your water contains. The “dirtier” your water is, the more wastewater there will be. However, you can help by making sure that pre-filters (sediment, carbon, etc.) are replaced regularly to help protect the RO membrane from premature loading. Making sure your system is running at the recommended PSI level (35 to 40 psi) will also assist in reducing wastewater levels. You can use a booster pump to correct lower pressure levels. In addition to regular cartridge replacement and membrane replacement, keeping your system maintained and in working order keeps wastewater levels lower. This includes making sure the system is clean and that any worn out valves or other parts are replaced.

Yes! You can have a professional help you, or you can very carefully redirect the wastewater to a storage tank, outside to a bucket or other collection source, or to another faucet such as an outdoor faucet or hot water faucet that is not used for drinking. Since the wastewater contains a high concentration of contaminants, it should not be used for certain things, such as drinking, bathing, pet care, and cooking. But the collected wastewater can be used for other purposes like watering plants, household cleaning such as the bathroom or outdoor masonry and paths, flushing toilets, pre-soaking laundry, decorative fountains, evaporative coolers, and more.

Any system that claims to be less or zero waste just redirects the wastewater elsewhere, but it definitely still produces wastewater. Some systems direct the wastewater back through the system, but this can cause filters to wear out at a higher rate than systems that do not as the contaminants continuously run back through the filter media. Other systems send the wastewater to the hot water tank in the home instead of the drain saddle. While this method does reduce waste, it also means that all of the contaminants are now in your hot water that you use for showering, washing hands, cleaning dishes, and laundry.