Every RO purifier sends part of the incoming water to the drain – this reject water carries away the salts the membrane removed. In a typical home that can add up to many litres a day. The good news: most of it can be reused.
Collect it first
Put the RO drain pipe into a bucket or a small container instead of the sink drain. Some people connect it to a larger can with a tap. Keep it covered so it stays clean.
10 ways to reuse RO waste water
- Mopping floors – one of the best uses; it cleans well.
- Toilet flushing – pour it into the flush tank or bucket.
- Washing vehicles – cars, bikes and scooters.
- Cleaning balconies, stairs and courtyards.
- Pre-rinsing utensils before the final wash with normal water.
- Washing clothes – mixed with normal water, for regular laundry.
- Desert cooler – works, but expect more scaling on the pads; clean them more often.
- Construction and cleaning work – mixing, washing tools.
- Watering salt-tolerant plants – dilute with normal water and watch the plants.
- Rinsing mats, buckets and dustbins.
What NOT to use it for
- Drinking or cooking – it has a higher concentration of salts than your tap water.
- Bathing small children or washing the face if your input water is very hard.
- Watering sensitive plants continuously – high TDS can harm soil and plants over time.
- Aquariums.
How to reduce the waste itself
- Replace pre-filters on time – choked filters make the purifier run longer.
- Use the correct flow restrictor for your membrane.
- Replace a solenoid valve that lets water flow to the drain when the purifier is off.
- If your tap water TDS is already low, you may not need RO at all – see RO vs UV vs UF.
Frequently asked questions
How much water does an RO waste?
It varies with the purifier and water quality. Many domestic units send more water to the drain than they purify.
Is RO waste water harmful?
It is not toxic, but it has a higher level of dissolved salts, so it should not be used for drinking or cooking.
Can I use RO waste water for plants?
Only for salt-tolerant plants and preferably mixed with normal water.
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