Reverse osmosis (RO) wastewater, also known as brine or reject water, can be effectively repurposed for various non-potable applications, significantly reducing overall water consumption and promoting water conservation.
Understanding RO Wastewater
When a reverse osmosis system filters water, it separates clean, purified water from water containing concentrated dissolved solids, salts, and impurities. This concentrated water is the RO wastewater, which typically has a higher Total Dissolved Solids (TDS) content than the incoming tap water. While not suitable for drinking, its properties make it useful for many other purposes.
Practical Applications for RO Wastewater Reuse
Repurposing RO reject water offers an environmentally friendly way to conserve water within your home and garden.
1. Household Cleaning
RO wastewater is well-suited for various cleaning tasks, leveraging its availability without requiring potable water quality.
- Mopping and Scrubbing Floors: You can use RO reject water to mop and scrub floors. To ensure the best results and prevent any potential residue or stains, especially if your reject water has high TDS and salt content, it is highly recommended to dilute the wastewater with an equal amount of tap water. This simple dilution step helps to eliminate any residue and ensures a clean finish.
- Washing Cars and Outdoor Surfaces: It's an excellent option for washing vehicles, cleaning driveways, patios, and outdoor furniture. For car washing, it can be particularly useful for initial rinses or general cleaning where spotting is less of a concern.
- General Rinsing: Use it for rinsing dirty items before washing them in a dishwasher or laundry machine, helping to pre-clean and save treated water.
2. Toilet Flushing
One of the most straightforward and effective ways to reuse RO wastewater is for toilet flushing.
- Refilling Toilet Cisterns: Manually pouring RO reject water into your toilet's cistern (the tank at the back) saves a significant amount of potable water with each flush. This application does not require high-quality water, making it an ideal use for reject water.
3. Gardening and Landscaping
With careful consideration for the TDS levels and plant sensitivity, RO wastewater can support your garden.
- Watering Salt-Tolerant Plants: While high levels of dissolved salts can harm many plants, certain salt-tolerant species can thrive with RO reject water, especially when diluted. Examples include some ornamental grasses, oleander, or specific palm varieties. Always test the impact on a small section or a single plant first.
- Irrigating Lawns (with Caution): For lawns with good drainage and grass varieties known to tolerate slight salinity, diluted RO wastewater can be used. Regular monitoring for signs of stress or salt build-up in the soil is crucial.
- Compost Piles: Use the wastewater to keep your compost pile moist, aiding in the decomposition process.
For more information on managing soil salinity for your garden, consult resources like Gardening Know How on Soil Salinity.
4. Other Non-Potable Uses
- Firewood Soaking: For wood-burning stoves, soaking firewood in RO reject water can increase burn time and efficiency, as the dissolved minerals can help retain moisture.
- Evaporative Coolers: In some regions, RO reject water can be used in evaporative (swamp) coolers, though this requires careful monitoring to prevent excessive mineral build-up and scaling in the system.
Important Considerations and Best Practices
To maximize the benefits and ensure safe reuse of RO wastewater, keep these points in mind:
- TDS Levels Vary: The TDS concentration in your RO reject water depends entirely on the quality of your incoming tap water. Higher initial TDS means higher TDS in the reject water, which affects its suitability for certain uses.
- Dilution is Crucial: For applications like cleaning floors or watering plants, diluting the wastewater significantly reduces the concentration of salts and minerals, preventing potential damage or residue.
- Proper Collection and Storage: Collect RO wastewater in clean, covered containers to prevent contamination from dust, insects, or other debris. Store it in a cool, dark place if not used immediately.
- Avoid Potable Use: RO reject water is not purified water and should never be used for drinking, cooking, bathing, or any other application requiring potable water quality.
- Observe and Adapt: When trying new applications, especially for gardening, start small and observe the results. Adjust usage or dilution as needed.
Summary of RO Wastewater Reuse
| Application | Description | Key Consideration |
|---|---|---|
| Household Cleaning | Mop and scrub floors, wash cars, clean outdoor surfaces. | Dilute with equal parts tap water for floors to prevent residue/stains. |
| Toilet Flushing | Use to refill toilet cisterns manually. | Requires manual collection and pouring; no special treatment usually required. |
| Gardening & Landscaping | Water salt-tolerant plants, irrigate lawns (with caution), moisten compost piles. | Dilute significantly for most plants; high TDS can harm salt-sensitive species. Test TDS if unsure. Consult local gardening resources for salt-tolerant plant lists. |
| Other Non-Potable Uses | Soaking firewood, general outdoor washing, evaporative coolers (with monitoring). | Monitor for mineral build-up in appliances (e.g., evaporative coolers). |
By responsibly reusing RO wastewater, households can make a meaningful contribution to water conservation and environmental sustainability. For broader tips on saving water at home, visit the EPA WaterSense program.
