Interactive Calculator · 2026
RO Water Wastage Calculator
See how much water a domestic RO purifier rejects for the purified water you use. Enter the litres you drink and cook with each day and your unit's recovery ratio — get the feed water it draws, the reject it dumps and your monthly wastage.
Every litre purified draws 4 L of feed water
Your RO usage
The permeate — the clean water your family actually drinks and cooks with each day.
The share of feed water that becomes purified water. Most domestic RO units recover only ~20–35%; better membranes and reject-recirculation designs push higher.
Purified vs reject — how your feed water splits
Of the 80 L drawn each day, only 20 L is purified — the rest is rejected.
At 25% recovery your RO throws away about 3 litres for every litre it purifies. But this reject is not sewage — it is simply higher-TDS water, perfectly good for mopping floors, watering salt-tolerant garden plants, flushing toilets and pre-washing.
Capturing the reject in a bucket or a diverter line roughly halves the effective waste — and higher-recovery or reject-recirculation units waste far less to begin with.
How this is calculated
- Feed water = purified ÷ (recovery ÷ 100) = 20 ÷ 0.25 = 80 L/day.
- Reject (wastage) = feed − purified = 80 − 20 = 60 L/day.
- Reject ratio = reject ÷ purified = 60 ÷ 20 = 3:1.
- Monthly wastage = reject × 30 ÷ 1000 = 60 × 30 ÷ 1000 = 1.8 kL.
Indicative figures for concept planning — real reject depends on membrane condition, feed TDS, pressure and temperature. Confirm against your unit's rated recovery and a qualified technician before sizing storage or a reuse line.
Frequently asked questions
- How does the RO water wastage calculator work?
- It works from two inputs — the litres of purified water your family uses each day and your unit's recovery ratio. Feed water is your purified litres divided by the recovery fraction, so at 25 percent recovery drawing 20 litres purified needs about 80 litres of feed water. The reject or wastage is feed water minus purified water, and it also shows the reject-to-purified ratio and monthly wastage in kilolitres.
- What recovery ratio should I enter for a home RO purifier?
- Most domestic under-counter RO units recover only about 20 to 35 percent, so a default near 25 percent is realistic for planning. Older or poorly maintained membranes recover less. Some newer units with reject-recirculation or booster designs claim higher recovery. Check your purifier's rated recovery in its manual or with the manufacturer rather than assuming, since actual recovery also drops as feed TDS, pressure and temperature vary.
- Can I reuse RO reject water at home?
- Yes. RO reject is not sewage — it is simply higher-TDS water, perfectly usable for mopping floors, flushing toilets, pre-washing utensils or cars, and watering salt-tolerant plants. Capturing it in a bucket or a diverter line roughly halves your effective waste. Avoid using it for drinking, for cooking, or on salt-sensitive plants, and let a professional advise before plumbing a permanent reuse line.
Related Guides — Deep-dive reading
Domestic Water Treatment Guide for Indian Homes: Test First, Then Treat Right
A master overview of treating the water coming into an Indian home — how to test first, match each contaminant to the right treatment, choose point-of-use versus point-of-entry, build a treatment train in the correct order, avoid over-treating, and budget for maintenance and running cost.
PlumbingHome Greywater Recycling Systems: Simple Reuse at Home
How a single house can recycle its bath, basin and laundry water for flushing and gardens — without a full sewage treatment plant. What to build, how to size it, where to reuse it, and the mistakes that turn a clever system into a smelly one.
Sewage Treatment PlantsRO vs UV Water Purifier: Which One Does Your Home Need? (India)
A fair, India-first head-to-head decided by one number — your feed-water TDS. RO strips dissolved salts and heavy metals for hard borewell water; UV only kills microbes and suits already-clear, low-TDS municipal supply. What each removes, water wastage, running cost, and a verdict by measured TDS.
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