Plumbing question. Can I use this as a drain for ro/di?

lubeck · Dec 30, 2021

I have a water spout in the garage for my water softener. I’m assuming it’s okay to hook up my ro unit to this but I’m wondering if the pipe to the left is a drain I can use for the waste water? It’s the hole going into the house, left of the red tube? Also, Does anyone know if the water source going into the ro unit is pre- or post softener?

thanks

jassermd · Dec 30, 2021

Supply line: I would assume the faucet is tap water and is feeding the water softener. If that's the case, then yes, I would reckon you can use that as the supply for your ro/di system.

As for before/after: Installing the rodi before the softener will deplete your DI resins a little faster. Installing the rodi after the softener may help prevent scale formation on the membrane. The softener may help remove some iron from the water which is hard on rodi membranes.

Now for the drain... water softeners work similar to ro membranes and they will need to discharge water similar to a ro/di system. Assuming that yours works in this manner, the black hose coming from the softener to the wall (and as you said, entering the house) is likely making it's way to a drain line. If that's the case, I would recommend following that line and determining where it is dumping and then installing your ro/di discharge line there. I would hesitate installing the ro/di drain line into the softener discharge line directly as you don't know the pressures and if there is a pressure gradient, you could get backflow into one or the other.

lubeck · Dec 30, 2021

Hmm. Thanks for the reply. how would I go about “following the line”? I do remember hearing water go thru the black hose and into the house when it going thru a cycle. There is also an air gap between the black hose and the copper line so it shouldn’t be pressurized. I could hear water dumping into it.

lubeck · Dec 30, 2021

See the air gap I would go directly into the house not the softener

jassermd · Dec 30, 2021

I've plumed and installed a water softener, so I would be willing to bet that hose runs to a drain inside the wall, or nearby.
Ideally, you can use a camera to see inside without damaging the wall and then cutting only where you need to.
If that's not an option, I would cut out a section of drywall to find where that drain runs. Drywall is easy to fix.
The drain is likely close by... do you have a bathroom or laundry room on the other side of the wall? Or any plumbing on the other side of the wall? If so, that's likely where it goes. That black hose ties into a drain nearby...
You could try to tie into the black hose directly close to where it elbows. Given that it's a drain, it won't go uphill without pressure, so you should be ok from the ro/di drain perspective. My concern would be when the softener drains, it could backflow into the ro/di filter and that would not be good. Softeners drain quite a bit and although not pressurized per se, it is a fairly decent volume with a good flow. You could put a check valve in the ro/di drain line to prevent the backflow.