Plumbing reverse osmosis filter runoff into water heater?

Mengsk · Nov 3, 2018

For those unaware, RO water filters like we use for hydroponics have a runoff or waste stream the way they work. The majority of the water used ends up as 'waste' or bypassing the filter. I can't think of a practical use for that (i.e. what to do with another 40-50 gallons of 'unfiltered' water in addition to the 10-15 gallons of RO water each time).

Anyone here have experience making use of the runoff? I'd like to feed it back into my home water system, like the washing machine or water heater.

Palindrome · Nov 4, 2018

You risk massive build-ups in your home applience, if you use the waste water from your RO filter.

It contains most of the ion's removed from the RO water, to keep the RO membrane working. If you then put that into your water heater, it will result in a thick coating on your heater if your lucky. Worst case, it will stick to the inside of the pipes as well.

I think the best option, would be mix with rainwater and water your lawn or something with it.
If thats an option, if not I think the best option is down the drain.

MJPassion · Nov 4, 2018

Put it in a pot on the fireplace to keep the humidity in the house up over the winter. You'll see how much crap you are actually filtering out. :biggrin:

In the summer water the bushes around the house but don't put it on the garden unless you are already starting with low PPM tap water.

It works well for flushing the toilet too.

Douglas.Curtis · Nov 4, 2018

Change your output restriction to a 1:1. You'll get about 1 gallon of 'waste' for every gallon of r/o.

Waste not the correct word for the higher ppm output water, unless you actually waste it.

I do what Palindrome suggests and use it on gardens and lawns. I've been known to wash clothes in it as well.

BakedBandit · Nov 4, 2018

Douglas.Curtis said:
Change your output restriction to a 1:1. You'll get about 1 gallon of 'waste' for every gallon of r/o. Waste not the correct word for the higher ppm output water, unless you actually waste it.

I do what Palindrome suggests and use it on gardens and lawns. I've been known to wash clothes in it as well.

This will shorten the life of your membrane. The best way to get less waste is to use multiple membranes in series. This requires you have good incoming pressure, and or a booster pump. But it is worth it. You get more product water out of the prefilters before needing to change them this way as well.

BakedBandit · Nov 4, 2018

Mengsk said:
For those unaware, RO water filters like we use for hydroponics have a runoff or waste stream the way they work. The majority of the water used ends up as 'waste' or bypassing the filter. I can't think of a practical use for that (i.e. what to do with another 40-50 gallons of 'unfiltered' water in addition to the 10-15 gallons of RO water each time).

Anyone here have experience making use of the runoff? I'd like to feed it back into my home water system, like the washing machine or water heater.

It depends a lot what your starting water quality Is like. Keep in mind that yes the waste water has been concentrated a little with things the membrane rejects, but that it has also been filtered before it reaches the membrane, so in some ways it is cleaner than the incoming tap water. It is usually just fine for trees or lawns in my experience, but I have pretty good quality starting water.

Douglas.Curtis · Nov 4, 2018

BakedBandit said:
This will shorten the life of your membrane. The best way to get less waste is to use multiple membranes in series. This requires you have good incoming pressure, and or a booster pump. But it is worth it. You get more product water out of the prefilters before needing to change them this way as well.

I had not thought of this, but I do see how it would work. Changing a membrane early is not a big deal, vs the amount of extra water I'd be using. Definitely will look into the multiple membrane idea though, water pressure here is 100+psi.

BakedBandit · Nov 4, 2018

Douglas.Curtis said:
I had not thought of this, but I do see how it would work. Changing a membrane early is not a big deal, vs the amount of extra water I'd be using. Definitely will look into the multiple membrane idea though, water pressure here is 100+psi.

That's awesome! You can probably run 2-3 with that pressure. Most membranes don't want to be run higher than 80-90 btw. Having the proper flow restrictor is still a good idea tho.

Switcher56 · Nov 4, 2018

Mengsk said:
For those unaware, RO water filters like we use for hydroponics have a runoff or waste stream the way they work. The majority of the water used ends up as 'waste' or bypassing the filter. I can't think of a practical use for that (i.e. what to do with another 40-50 gallons of 'unfiltered' water in addition to the 10-15 gallons of RO water each time).

Anyone here have experience making use of the runoff? I'd like to feed it back into my home water system, like the washing machine or water heater.

The by product is concentrated sludge for the lack of a better word. When dealing with sea water the by product is known as BRINE, which deserves to go back to the sea. What you do on land is up to you. There is a reason it gets disposed of

Gry · Nov 5, 2018

Interesting subject.

MJPassion · Nov 5, 2018

DBl post

MJPassion · Nov 5, 2018

Douglas.Curtis said:
Change your output restriction to a 1:1. You'll get about 1 gallon of 'waste' for every gallon of r/o. Waste not the correct word for the higher ppm output water, unless you actually waste it.

I do what Palindrome suggests and use it on gardens and lawns. I've been known to wash clothes in it as well.

BakedBandit said:
This will shorten the life of your membrane. The best way to get less waste is to use multiple membranes in series. This requires you have good incoming pressure, and or a booster pump. But it is worth it. You get more product water out of the prefilters before needing to change them this way as well.

You can install a bypass valve that will flush the membrane for longer life.

And membranes are connected in parallel not in series.
What's the point of running your RO through another RO membrane?

BakedBandit · Nov 5, 2018

MJPassion said:
You can install a bypass valve that will flush the membrane for longer life.

And membranes are connected in parallel not in series.
What's the point of running your RO through another RO membrane?

You run the waste from the first to the input of the next. You make almost double the product water with close to half the waste, and basically doubles the usable life of your prefilters since you are running all of the waste water through them as well.

MJPassion · Nov 5, 2018

Interesting.
>scratches head<
I guess that would work but the second filter would suffer a shortened life cycle due to filtering an elevated ppm source water.
By running the RO membranes in parallel with one another their life span would be the same.

BakedBandit · Nov 5, 2018

It's faster that way, But you don't save any water and go through more prefilters, and the contact time with said prefilters will be shorter so they will less effective. If you don't get all the chlorine/chloramine out before it hits the membrane it will ruin it rather quickly.
I have used membranes in series for many years now, it works great.

Mengsk · Nov 5, 2018

I think the takeaway is it isn't an exact science and I did not think the waste water had much higher ppm. Drinking water, washing your hands or taking a shower, watering the garden, laundry, washing your car, and pouring filtered water straight down the drain these are all very different things. Bottled water you buy from the store is filtered water.

Switcher56 · Nov 5, 2018

Reverse Osmosis desalination is designed for the desalinating sea water. The waste water is highly concentrated brine, which you dispose of. Tap water, well that is another Q. That being said, collect it and use in you garden if safe to do so. The equipment wasn't designed to recycle waste water. Let alone giving your system the "dble wammy"

Absolem · Nov 5, 2018

BakedBandit said:
You run the waste from the first to the input of the next. You make almost double the product water with close to half the waste, and basically doubles the usable life of your prefilters since you are running all of the waste water through them as well.

Agreed^^^^^

I run two membranes on my RO unit. Saves on the waste and almost doubles the output. It's called "waste water staging" and is quite common. Here's a great video on how to do it.

https://www.youtube.com/watch?v=GE0Dhp5DZv8

PetFlora · Nov 6, 2018

Mengsk said:
I think the takeaway is it isn't an exact science and I did not think the waste water had much higher ppm. Drinking water, washing your hands or taking a shower, watering the garden, laundry, washing your car, and pouring filtered water straight down the drain these are all very different things. Bottled water you buy from the store is filtered water.

While the VOCs are filtered out, you would ned to check the PPM/TDS/EC of your runoff before deciding what to do with it besides letting it go to drain

Plumbing reverse osmosis filter runoff into water heater?

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