How much water does an RO purifier waste?

Reverse osmosis needs pressure. Water is forced against a membrane, some passes through, and everything rejected has to be flushed away — carrying the concentrated contaminants with it.

That reject stream is not a fault. It is how the process works. Without it the membrane would clog within days.

The ratio

A typical domestic RO recovers around 40% of the water it takes in. The other 60% goes to the drain. Put plainly: for every glass you drink, roughly three go down the sink.

Capacitive deionisation does not rely on pressure against a barrier, so it does not need to flush at anything like the same rate. Recovery of up to 70% is achievable — close to double.

What that looks like over time

Take a household drinking about eight litres of purified water a day — a family of four, unremarkable. Over five years that is roughly 14,600 litres consumed.

At 40% recovery, producing it costs about 36,500 litres, so nearly 22,000 litres go to waste. At 70% recovery, waste drops to about 6,300 litres.

The difference is in the region of 15,600 litres over five years. If that is hard to picture, it is roughly 50 trees' worth of water for a year, or about 195 showers.

Why this is becoming harder to ignore

India's groundwater is under real pressure, and domestic purification is not the largest cause of that. But a technology that discards 60% of what it touches is a strange default to have settled on, particularly when the alternative exists and performs the same job.