What to Do With RO Reject Water
Quick answer: Every RO plant splits feed water into product water and reject (concentrate) that carries the removed salts. The share depends on the plant's recovery: at 50% recovery, one litre of reject for every litre of product. Reject is not for drinking, but it can often be used for toilet flushing, floor and vehicle washing and construction; irrigation depends on how salty it is.
Key facts
- Reject carries the salts RO removes
- Volume depends on recovery
- Good uses: flushing, washing, construction
- Test salinity before irrigating
On this page
How Much Reject Will I Get?
Reject = feed water − product water. A plant at 50% recovery makes one litre of reject per litre of product; at 65% recovery about half a litre. Recovery is set by the water analysis to avoid scaling. Work it out with the RO plant size calculator.
Good Uses for Reject Water
- Toilet flushing (pipe it to a separate tank).
- Floor, yard and vehicle washing.
- Construction: mixing and curing, where the contractor accepts it.
- Cooling and some cleaning processes.
Use With Care
- Irrigation: concentrated salts can harm soil and sensitive crops. Test TDS first; dilute or use on salt-tolerant plants only.
- Livestock: only if the TDS is suitable; see water for livestock.
- Never sell or drink it.
Reducing Reject
- Good pre-treatment and antiscalant let the plant run at higher recovery: antiscalant.
- Softening hard water before RO can help.
- For municipal water that is already low in salt, UF may suit instead of RO: RO vs UF.
Disposal
Large plants need a planned outlet; check county and Water Resources Authority (WRA) requirements for discharge.
Htech 250LPH RO PURIFIERKSh 290,000
Htech 500lph Ro water purifierKSh 380,000
Htech 750lph Ro purifier plantKSh 500,000| Product | Price |
|---|---|
| Htech 250LPH RO PURIFIER | KSh 290,000 |
| Htech 500lph Ro water purifier | KSh 380,000 |
| Htech 750lph Ro purifier plant | KSh 500,000 |
Current listed prices incl. VAT (updated 5 October 2026).
Watch: RO purifiers and water ATMs
Frequently asked questions
What is RO reject water?
The concentrate stream that carries away the salts the membrane removes.
How much reject water does RO produce?
It depends on recovery: about one litre per litre of product at 50% recovery.
Can RO reject water be used for irrigation?
Only after testing its salinity; it can harm soil and sensitive crops.
Is RO reject water safe to drink?
No, it contains the concentrated salts removed from the water.