How Much Water Does Reverse Osmosis Use? Learn to Compare Its Efficiency
One of the most common questions about reverse osmosis is how much water the process “wastes.” It is a valid question, but understanding it precisely helps you compare equipment.
Why the process produces reject water
Reverse osmosis separates water into two streams: treated water, which passes through the membrane, and reject water, which carries the separated substances. That second stream is necessary for the process, rather than an equipment defect. Source: EPA
Without reject water, retained substances would accumulate at the membrane and reduce its lifespan and performance.
What “efficiency” means here
A reverse osmosis system’s efficiency is commonly expressed as the relationship between treated water produced and total water used, including reject water.
This relationship varies considerably between models according to design, incoming pressure, and pump technology where a pump is included. Source: EPA
Ask for the specific model’s ratio in clear terms—for example, liters of reject water for each liter of treated water.
WaterSense as a reference
The EPA’s WaterSense program sets efficiency criteria for point-of-use reverse osmosis systems, considering both dissolved-solids reduction and water use. If a product claims this label, confirm that it applies to the exact model. Source: EPA
Factors that affect efficiency
- Incoming water pressure at your installation.
- Whether the system uses a pressure-boosting pump.
- Membrane and drainage-system design.
- Incoming water temperature.
These factors can differ between installations. Advertised efficiency reflects specific test conditions, not necessarily the exact result in your home.
Compare with information, not assumptions
Instead of assuming all reverse osmosis systems use large amounts of reject water, request the efficiency ratio of the model you are considering and compare it with other options under similar conditions.
At PFC, we share this information so you can assess our systems using specific data.
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