Can I use the A/C condensate drain as the drain for a reverse osmosis system? Would I need a one-way valve on the reverse osmosis line? Someone mentioned an "air gap". What is this.

  • Are you running the condensate through the RO system? Please edit for some clarity. Remember, we only know exactly what you tell us, and if you leave us to make assumptions, well, we might make the wrong ones.
    – FreeMan
    Commented Jan 9 at 16:06
  • Is this RO being used for potable cold water or is being used to treat only the cold feed water of a water heater? Commented Jan 9 at 16:58

2 Answers 2


I presume what you're asking is whether the reverse osmosis system's waste line can drain into the existing condensate drain.

My dehumidifier was draining into the same pump my condensing boiler was; the pump then pushed that water to a drain and out of the house. It sounds like that's similar to what you're trying to do here.

There's nothing inherently unreasonable about the idea. I'd want to have an air gap to guard against back flow; simpler than putting in a check valve.

Be aware that you are going to put more load on the pump, so it will wear out sooner.


You need more than a one-way valve

I would expect that the PVC condensate line is large enough, but you need an air gap to prevent backflow. This is potable water stuff, please don't mess around with it. My personal level of comfort with air gaps is it's fine for your dishwasher but not for a system you drink from. I would probably have a plumber do this for me, my plumbing knowledge is I've sweated copper about 5 times in my life and am comfortable under the sink.

Your local codes will specify this, and I would expect that the device will have instructions as well.

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