RO explained (C) Daniel Friedman Reverse Osmosis Water System Waste Impact on Septic Systems - Septic Tank Maintenance

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Reverse Osmosis water purifier effects on a septic system: Does a home reverse osmosis water treatment system damage the septic system by the disposal of its concentrate water into the septic tank?

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Reverse Osmosis Water Treatment Systems Impact on Septic Tank and Drainfield

Reverse Osmosis POU System (C) Daniel FriedmanThe good news is that reverse osmosis for water purification does not rely on chemicals that may be toxic when released in the environment. Reverse osmosis or RO water treatment systems work by passing water through a membrane that keeps contaminants on one side.

The down-side risk of high levels of reverse osmosis use in a property served by a septic tank and drainfield is that the system might be releasing an un-wanted quantity of additional water into the drainfield.

Reverse osmosis or R.O. water purifiers waste about four gallons of water for every gallon of purified water that they produce.

In normal use with a small point-of-use (POU) RO system (photo at left) such as one providing just a few gallons of purified water per day at a kitchen sink, the impact on a septic system is negligible.

But a large RO system may be a problem if the effluent absorbing capacity of the drainfield is limited.


RO explained (C) Daniel FriedmanSome designers or water treatment equipment providers such as Watts suggest routing the waste water produced by a reverse osmosis system back to the building plumbing system as gray water used for washing, bathing, or flushing toilets.

If you take this approach you can reduce the water waste from your R.O. system, possibly to zero.

If you plan to purchase a system that recycles wastewater from an RO water purifier, make sure that your system meets local plumbing codes - some systems, especially ones that do not further filter or treat the wastewater before it is recycled do not meet plumbing codes in some areas.

More information about Reverse Osmosis for water treatment and purification can be found at Reverse Osmosis.

Reverse Osmosis Systems - Impact on Septic Systems and Water Quantity Usage

What about water volume from reverse osmosis water treatment systems? These can vary by manufacturer with a range of 3:1 to 10:1 of waste to product efficiency.

"Typically" for every gallon produced with a top of the line system, 3 to 5 gallons goes into the septic tank. Less efficient systems (regardless of shutoffs) can dump up to 10 gallons to waste for every gallon that goes into the storage tank. Don't despair...the membranes of ten years ago dumped up to twenty five gallons per gallon of product.

Ask the manufacturer of your reverse osmosis water treatment system for their efficiency, platform statement, and percent recovery data.

An excellent resource for membrane information is the National Sanitation Foundation. We are not confident about the generalized water quantity usage information obtained via EPA publications, Small Flows, etc.

If you ask reputable reverse osmosis treatment system manufacturers, you should be able to get reliable water usage and water flow information. -- Larry Newcomb Encinitas Learning Center

[Thanks to Larry Newcomb Encinitas Learning Center,, for the above opinion--DJF]

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