Traditional household RO can send several gallons to drain for each gallon purified, while efficient modern systems can approach roughly 1:1 or better under favorable conditions. Compare the exact tested recovery or pure-to-drain ratio, not generic RO assumptions.
What the ratio means
A 1:1 pure-to-drain ratio means roughly one gallon of reject water for every gallon of purified water. A 3:1 pure-to-drain claim means about three gallons purified for one gallon rejected.
Marketing conventions can reverse the order, so always confirm which number represents purified water.
Why pressure matters
RO membranes work more efficiently with adequate feed pressure. Low pressure can reduce permeate production and worsen practical recovery, which is why many tankless systems use booster pumps.
Automatic flushing changes real-world use
Some systems flush the membrane before or after production. Those flush cycles may not be captured by a simple headline membrane ratio, so actual household drain volume can differ.