Installing RODI system

[LorenK]

I have a 24g/day RODI system.

I know how to tap into my water line in my house for the input. I'm curious if it is possible to put my output (waste water) back into my water system. Given it's a 24g/day unit, there is a lot of waste water in comparison to clean water.

It's only 24g/day, the waste water is not much higher in TDS than my normal water. Also, we don't drink our water without it going through the kitchen filter so I'm not particularly concerned with a slight increase.

The problem I am trying to figure out is that once it's a closed loop with the house water, I think it will only produce filtered water when someone is using water in the house (showers, laundry, dishes, etc). I was thinking to put a switch to allow me to run the waste water outside in case I need to make water when needed to my back yard.

Also, how can I plumb it back into the water line so that the water only goes one way? Can I use a check valve for that?

Has anyone setup their system like this?

[ericmcj31]

I'm not sure you can do that? Maybe someone else has more insight

[mojo]

If I understand you correctly, you're looking to put the water right back into your pressurized system, not just drain it out.

There are check valves for john guest fittings, but I've never seen anyone use them. Besides, I think there's a check valve in the restriction piece before it leaves the R/O unit.

My guess is that, without some kind of pressure pump, you won't be able to overcome the pressure of the intake (which is the same). You'll hook up the intake of the RO, and the output will be the same pressure, so it'll just equalize, and nothing will happen.

[ericmcj31]

maybe a better choice would be to plumb to a holding tank so you can use it to wash clothes, water shrubs, etc.-imo

[Gwhiz]

I can't think of any easy way to accomplish this. Even with a pressure pump to overcome the house pressure, you'd need some sort of storage because there's no holding tank 'cause there's simply no place for the water to go if water's not running in the house.

I've hear of using the waste water to fill washing machines, toilet tanks, etc. or outside into flower beds, etc. but haven't read about running it back into the house water.

But if you figure it out, let us know!

[LorenK]

I have a feeling it's not possible/feasible due to the pressure.

[mojo]

What would happen if you used a pressure pump on the intake and adjusted it so that pressure across your membrane was still 60-80 psi? This should keep pressure high enough to be pushed back into your house...

That's almost worth trying... hmm....

[Stanfill Reef]

This is a BAD idea. The RO/DI system will be a good breeding ground for bacteria. These would then be sent back into your house plumbing. If you are pulling out of the house system and putting back into the house system, the your plumbing from the road will only make up the difference that goes to your RO container, in other words you will basically be filling up your plumbing with dechlorinated, bacteria filled water while running the RO/DI...YUMMY. Can't wait to take a shower in that!

[ericmcj31]

I'd be more worried about drinking/cooking water--seems like the amount put back in would be minimal--it's only a 24 gpd unit

[KRB]

this is not what you want to do. It would require a strong pump to add additional pressure to your system while returning the waste water. I installed my unit in my laundry area and run the waste either down the washing machine drain or use it to fill my washing machine.

[tnyga]

Give it to your garden

[mojo]

This is a BAD idea. The RO/DI system will be a good breeding ground for bacteria. These would then be sent back into your house plumbing. If you are pulling out of the house system and putting back into the house system, the your plumbing from the road will only make up the difference that goes to your RO container, in other words you will basically be filling up your plumbing with dechlorinated, bacteria filled water while running the RO/DI...YUMMY. Can't wait to take a shower in that!

The house water system would be flushed every time someone turned on a faucet, took a shower, flushed a toilet, etc. Also- I'm not sure where these bacteria you speak of are coming from - do you have any references to support this? Water comes in chorlinated, goes through a cotton prefilter, a carbon block filter, over an RO filter (but not through) and back into the house system... where exactly do these backteria live and thrive?

Maybe put a UV sterilizer on the output side, back into the house, if that were the issue.

Also- there are drinking kits available for all RO units. The drinking kit hooks up after the RO membrane and before the DI membrane. If there were bacteria in there, then every one of these DI kits could also be a breeding ground for bacteria.

Originally Posted by KRB

this is not what you want to do.

I don't know... my water bill last month was $170... I'm pretty motivated.

[reefknight]

When I was setting my RO system up I called a friend who is a plumber. I wanted to attach my RO drain to the overflow safety drain of my hot water heater. He told me several things at the time of how this should not be done under any circumstances, and that it was considered a major building code violation. Had to do with the water backing up into the water mains and something to do with bacteria being intorduced into the water mains. He quoted a study to me at the time, but I never got around to lokking it up. The only method that of hooking RO waste water that is acceptable is to a drain line that goes to a sewer (washing machine, sink drain, etc.)

This is just what I can remember him telling me at the time, and that was well over a year ago. I trust his views as he is my personal and proffesional plumber and does many major buisness in the middle GA area. I hope this helps!

[mojo]

Hmm.... well.... that sucks. I guess I'll find a better use of the RO waste line...

[reefknight]

I had a hard time growing grass around my A/C unit and one side of my house. So I ran the line over there to a soaker hose by "engineered" a few fittings together. I have grass there now!

[Stanfill Reef]

The bacteria will live in your RO membrane on the dirty water side. The carbon block removes the chlorine so that there is no disinfection. The membrane is concentrating the bad stuff on the dirty water side, including the organics in your water. The membrane surface (and actually the surface of the activated carbon too) now has a food source and no disinfection, perfect little bacteria breeding ground. The bacteria will not go through the membrane to your clean water because of the membrane, but the reject/dirty water pass on any bacteria from the carbon and membrane surface. In industrial applications you would wash the membrane every so often to remove the bacteria and other foulants using either acid or chlorine, depending on the type of membrane.

Even beyond the bacteria think about this: you would fill 1046 linear feet of 3/4" pipe with 24 gallons of water. For 1" pipe it would be 589 linear feet. So if you assume that your RO/DI wastes 4 gallons for every 1 gallon of treated water you produce, you would need over 4000 linear feet of pipe. So if you put the water back into your water line you would likely just be pumping the same dirty water around and around and around your RO/DI system making it much dirtier with each pass. Still a bad idea.

Use the water somewhere else. Turn your toilets off at the wall, fill a container with RO/DI reject, and use it to refill your toilets when you flush. Water your houseplants. Wash your dark clothes. Wash your dog. But don't use the reject water for bathing or food.

[mojo]

Interesting - that all makes sense....

Oh well, and I thought solved it my water problems...

[LorenK]

You all have made good points...I'm going to find another use for the water.