How this calculation works
Collect both streams over the same interval. Their sum is measured feed. Recovery divides product by that sum; daily demand scales runtime, water input and active electrical consumption.
Recovery = product / (product + reject); daily feed = daily product / recoveryA worked example
Collecting 2 L product and 6 L reject gives 25% recovery. Producing 12 L at the measured rate needs 48 L feed, generates 36 L reject and takes one active hour.
Good to know
Constant-rate operating estimate only. No water-quality, potable-use or safe reject-reuse conclusion. Filter replacement, flushing, standby power, sewer fees and changing pressure are excluded.
Reference: US EPA WaterSense: point-of-use reverse osmosis systems (opens in a new tab) ↗
Use all measured feed in the denominator
Product plus reject forms the two-stream measured feed balance. Product divided by reject is a ratio between outputs; it is not recovery. Mixing those definitions can make comparisons misleading.
For two litres product and six litres reject, product/reject is one third while recovery is one quarter. The figure shows both outputs beside the combined feed so the distinction is explicit.
The repeated aquarium water change dilution calculator adds model unequal successive drain-and-refill changes with source-water concentration, a step table, total water use and an interactive concentration graph. The water leak meter night test cost calculator adds subtract known usage from a timed water-meter difference, show resolution bounds and estimate the incremental bill through entered cumulative tariff tiers.
Match the measurement interval
Measure streams at the same time under representative operating conditions. Comparing product collected over ten minutes with reject collected over five would distort both recovery and the daily projection.
The runtime uses the measured product rate. A request that would need more than 24 active hours per day is rejected. That check does not account for automatic flushes, storage behavior or changing inlet conditions.
Separate operating arithmetic from treatment performance
The cost combines feed-water price per thousand litres with active electrical energy. A wattage is power; multiplying it by runtime and dividing by one thousand gives kilowatt-hours.
A favorable recovery or running cost does not show that treatment is effective or that reject water is safe for a particular reuse. Water-quality decisions require their own evidence beyond the volumes entered here.
Use the result with the next measurement
The water leak meter night test cost calculator separates known use from unexplained meter movement over time. Keep RO feed use in the known-use record if the purifier operated during that interval.
Constant-rate operating estimate only. No water-quality, potable-use or safe reject-reuse conclusion. Filter replacement, flushing, standby power, sewer fees and changing pressure are excluded.
A few questions, answered
Is recovery product divided by reject?
No, it is product divided by product plus reject.
Does cost include filter replacement?
No, it includes entered feed-water and active electricity costs only.
Can this tell whether the water is safe?
No, volume balance does not measure quality.