Water treatment · Reverse osmosis
Reverse osmosis waste water calculator.
Turn your system’s waste ratio or recovery rate into gallons and dollars sent down the drain.
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Reverse Osmosis Waste Water Calculator: how it works
Recovery percent = product water / feed water. A waste ratio of R : 1 means R gallons go to the drain for each gallon of purified water, so recovery = 1 / (1 + R). A 3:1 system is 25% recovery; a 1:1 system is 50%.
Worked example. A 3:1 system serving 5 gallons of purified water a day sends 5 x 3 = 15 gallons to the drain and draws 20 gallons from the supply. Over a year that is 15 x 365 = 5,475 gallons wasted; at $6 per 1,000 gallons that is $32.85. Enter 25% recovery instead and you get the same answer.
Use your own numbers. The waste ratio varies by membrane, pressure and temperature, and by whether the system has a permeate pump. This tool does not assume a typical ratio: take it from your system's specification sheet, or measure the drain and product flow over the same time.
Frequently asked questions
What is a good RO waste ratio?
Check your maker’s specification. This tool does not assume a ratio; it shows what yours means in gallons and cost.
How do I convert a waste ratio to recovery?
Recovery = 1 / (1 + ratio). 3:1 is 25%, 2:1 is 33.3%, 1:1 is 50%.
How much goes to the drain at 50% recovery?
One gallon per gallon of purified water, a 1:1 ratio. At 25% recovery it is 3 gallons per gallon.
How do I measure my own ratio?
Collect the drain line and the product line in separate containers for the same time and divide drain volume by product volume.
Sources
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This tool is arithmetic on the numbers you enter; it uses only 365 days per year.
Runs entirely in your browser. Nothing you type is sent or stored.
Not professional advice
Arithmetic from the numbers you enter. Not a statement about a particular RO system’s performance. Not professional advice.