RO/DI waste water, what's in it, wrong with it and do you reuse it?

askolded · 01/10/2009, 11:46 PM

I've been using my home RO/DI unit for about 4 years now and changed the filters today (not for the first time! No flames please). After changing them out and while running through my normal 5-10 gals before using, I thought I would like to see just how must waste water is generated. Turns out its quite alot...3 or 4/1. Since I ran the waste into 5 gal buckets and just dumped them into my washing machine to lower my water use for laundry tomorrow. Is there anything wrong with this water? Its already been through 2 sediment filters, a carbon filter, an RO membrane (75gpd) and a resin bed. Its got to be the best wasted water on the planet....thoughts?

30reef · 01/11/2009, 12:38 AM

By waste water, do you mean the first 5-10 gallons of product water after you changed filters, or do you mean the waste water from the membrane?

If it's from the membrane, let it go down the drain. It is super concentrated with minerals. I would not use it to do laundry with. If it is the first few gallons of product water after a filter change, then you could use it for whatever you wanted to.

Hope that answered your question.

Puffdragon · 01/11/2009, 06:57 AM

I use mine to water plants or add to swimming pool.

EnglishRebel · 01/11/2009, 07:38 AM

Although I have one of these "water saving" RO/DI units The Filter Guys I too am concerned about wasting water. I intend to run my waste water to a 50g barrel outside so I can use it to top off my Koi pond or water plants.

BeanAnimal · 01/11/2009, 08:18 AM

Quote:

Originally posted by 30reef
By waste water, do you mean the first 5-10 gallons of product water after you changed filters, or do you mean the waste water from the membrane?

If it's from the membrane, let it go down the drain. It is super concentrated with minerals. I would not use it to do laundry with. If it is the first few gallons of product water after a filter change, then you could use it for whatever you wanted to.

Hope that answered your question.

Wait lets step back here....

Lets say you put 200 TDS into the RO/DI and you have a 98% membrane.

You make 5 gallons of product water and 25 gallons of waste water (1:4) product to waste ratio. That is a total of 30 gallons of water that started at 200 TDS

So you end up with 5 gallons of water @ 4 TDS and 25 Gallons of waste water at 239 TDS.

That watwer is perfectly safe to drink, do laundry with, water plants with, cook with, etc. It is not "toxic" or "poison" it is the same water that comes out of your tap.

What about 500 TDS tap water?

So 500 in becomes 5 gallons of 10 TDS product water and 25 gallons of 598 TDS waste water. Still not much worse than what you started with.

JNye · 01/11/2009, 08:31 AM

I make water based on when I need to do a load of laundry. I dump the waste water directly into the machine. The wife gets POed when I forget though, thats the only real danger.

aquaman67 · 01/11/2009, 08:59 AM

To add to what bean said, think about it.

Yes, the TDS will be a bit higher but the "waste" water from a RO/DI has gone through the pre-filter and carbon block. In some ways it is actually better than straight unfiltered tap water.

BeanAnimal · 01/11/2009, 11:06 AM

Quote:

Originally posted by aquaman67
To add to what bean said, think about it.

Yes, the TDS will be a bit higher but the "waste" water from a RO/DI has gone through the pre-filter and carbon block. In some ways it is actually better than straight unfiltered tap water.

Absolutely the particulate waste has been removed by prefilters.

30reef · 01/11/2009, 11:53 AM

I see what you mean. I guess I was basing my comments on the tap water here in Phoenix, it averages over 1000, in some months it is over 1500. So I try and not use tap water for anything, much less the RO waste water. I don't even want to dump it in the pool, there is already crust along the edge that is hard to get off. The softener helps but we sure do use alot of salt.

Thanks for doing the arithmatic, that does make sense.

AZDesertRat · 01/11/2009, 01:52 PM

The waste water, thats really a bda term for it by the way, has been through the prefilter and carbon so it will be low in particulates and wil have the chlorine and some organics removed. It will be 20 to 25% higher in TDS though since the TDS removed from the goodwater is added to the waste.
In some areas this may not be a problem but like 30reef said here in Phoenix and most of the southwest amd placesl like Florida and along some of the eastern seaboard TDS is quite high to begin with so concentrating it amkes the waste stream worse.
My TDS is over 800 so with a normal 4:1 I wouldn't even think of using the water in my washer or dumping it in my swiming pool. I use the Spectrapure MaxCap UHE system and its set at 1:1 waste ratio so its much higher so to the sewer it goes. It all gets treated and recycled anyway.

Back to the original post, when you changed filters I hope you didn't flush everything through the RO membrane and the DI, thats not a good idea at all!

When changing filters, remove the prefilter and carbon housings and toss the old filters, add 3 tablespoons of regular unscented bleach to the prefilter housing only and screw the empty housings back on. Now, very important, disconnect the line going from the last carbon up to the RO membrane housing at the membrane end and stick the line in a bucket or the sink. If its not long enough you can get a longer piece at the hardware for about 50 cents.
Turn the water supply back on and let the housings fill until you start to get water out of the line. Shut the water off and let things soak for a few minutes. Its important to note here that bleach is a very strong chlorine solution, 5% bleach is 50,000 parts per million so more is not better in this case, only 3 spoons and no more.
Now turn the water back on and let the water drain out the line for a few minutes or until the bleach smell has gone away. Turn things off, dump the water and install the new filters and while the line is still disconnected turn it on and bleed any wate rand air out of the system before hooking the line back up and you are done. This also flushes the new filters to remove any carbon dust or fines so they don't get to the membrane.

When changing the membrane flush it to waste with no DI resin or cartridge installed or disconnect the DI so you do not send high TDS water from the solutions membranes are coated with.

When changing DI flush it until you see 0 TDS.

askolded · 01/13/2009, 01:28 AM

AZ....to answer your question about how I installed my filters:
I just drained the whole system, removed the old cartridges , washed out the canisters and installed the 3 new cartridges plus a new RO membrane (did not change the resin). Then I started to run the system. Have I created any problems that can't be fixed?

Buckeye Hydro · 01/13/2009, 05:07 AM

Most vendors advise that you do something along the lines of what you did - but AZ is right. It is a better practice to flush each filter stage that needs it in order, installing the next after the previous is flushed so that you don't run "flush" water from one filter into the next filter.

Russ

01/10/2009, 11:46 PM	#1
askolded Registered Member Join Date: Jan 2007 Location: The Jersey Shore Posts: 32	RO/DI waste water, what's in it, wrong with it and do you reuse it? I've been using my home RO/DI unit for about 4 years now and changed the filters today (not for the first time! No flames please). After changing them out and while running through my normal 5-10 gals before using, I thought I would like to see just how must waste water is generated. Turns out its quite alot...3 or 4/1. Since I ran the waste into 5 gal buckets and just dumped them into my washing machine to lower my water use for laundry tomorrow. Is there anything wrong with this water? Its already been through 2 sediment filters, a carbon filter, an RO membrane (75gpd) and a resin bed. Its got to be the best wasted water on the planet....thoughts?

01/11/2009, 06:57 AM	#3
Puffdragon Registered Member Join Date: Nov 2005 Location: Indiana Posts: 297	I use mine to water plants or add to swimming pool. __________________ The definition of an expert "Someone who has done something for so long that they can not see a new way to do things." Current Tank Info: 350 gallon mixed reef system

01/11/2009, 07:38 AM	#4
EnglishRebel Retired Rebel Reefer Join Date: Sep 2005 Location: Triad NC Posts: 1,902	Although I have one of these "water saving" RO/DI units The Filter Guys I too am concerned about wasting water. I intend to run my waste water to a 50g barrel outside so I can use it to top off my Koi pond or water plants. __________________ Alan "Never in the field of human conflict was so much owed by so many to so few. " Sir Winston Churchill praising those young RAF pilots. August 20th 1940 Click on my name for drop down list and select "Visit EnglishRebels Home Page" for my build thread. Current Tank Info: 60x30x24 200G AO custom glass tank, basement equipment room, 30G and 55G Fuges, LifeReef sump & 30" skimmer.

01/11/2009, 08:31 AM	#6
JNye Moved On Up Join Date: Feb 2007 Location: Lansing, IL Posts: 2,230	I make water based on when I need to do a load of laundry. I dump the waste water directly into the machine. The wife gets POed when I forget though, thats the only real danger. __________________ Joe Current Tank Info: it don't matter just don't bite it

01/11/2009, 01:52 PM	#10
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	The waste water, thats really a bda term for it by the way, has been through the prefilter and carbon so it will be low in particulates and wil have the chlorine and some organics removed. It will be 20 to 25% higher in TDS though since the TDS removed from the goodwater is added to the waste. In some areas this may not be a problem but like 30reef said here in Phoenix and most of the southwest amd placesl like Florida and along some of the eastern seaboard TDS is quite high to begin with so concentrating it amkes the waste stream worse. My TDS is over 800 so with a normal 4:1 I wouldn't even think of using the water in my washer or dumping it in my swiming pool. I use the Spectrapure MaxCap UHE system and its set at 1:1 waste ratio so its much higher so to the sewer it goes. It all gets treated and recycled anyway. Back to the original post, when you changed filters I hope you didn't flush everything through the RO membrane and the DI, thats not a good idea at all! When changing filters, remove the prefilter and carbon housings and toss the old filters, add 3 tablespoons of regular unscented bleach to the prefilter housing only and screw the empty housings back on. Now, very important, disconnect the line going from the last carbon up to the RO membrane housing at the membrane end and stick the line in a bucket or the sink. If its not long enough you can get a longer piece at the hardware for about 50 cents. Turn the water supply back on and let the housings fill until you start to get water out of the line. Shut the water off and let things soak for a few minutes. Its important to note here that bleach is a very strong chlorine solution, 5% bleach is 50,000 parts per million so more is not better in this case, only 3 spoons and no more. Now turn the water back on and let the water drain out the line for a few minutes or until the bleach smell has gone away. Turn things off, dump the water and install the new filters and while the line is still disconnected turn it on and bleed any wate rand air out of the system before hooking the line back up and you are done. This also flushes the new filters to remove any carbon dust or fines so they don't get to the membrane. When changing the membrane flush it to waste with no DI resin or cartridge installed or disconnect the DI so you do not send high TDS water from the solutions membranes are coated with. When changing DI flush it until you see 0 TDS. Last edited by AZDesertRat; 01/11/2009 at 01:59 PM.

01/11/2009, 12:38 AM	#2
30reef Registered Member Join Date: Sep 2006 Posts: 1,401	By waste water, do you mean the first 5-10 gallons of product water after you changed filters, or do you mean the waste water from the membrane? If it's from the membrane, let it go down the drain. It is super concentrated with minerals. I would not use it to do laundry with. If it is the first few gallons of product water after a filter change, then you could use it for whatever you wanted to. Hope that answered your question.

01/11/2009, 08:59 AM	#7
aquaman67 Registered Member Join Date: Feb 2002 Location: Tennessee Posts: 7,629	To add to what bean said, think about it. Yes, the TDS will be a bit higher but the "waste" water from a RO/DI has gone through the pre-filter and carbon block. In some ways it is actually better than straight unfiltered tap water.

01/11/2009, 11:53 AM	#9
30reef Registered Member Join Date: Sep 2006 Posts: 1,401	I see what you mean. I guess I was basing my comments on the tap water here in Phoenix, it averages over 1000, in some months it is over 1500. So I try and not use tap water for anything, much less the RO waste water. I don't even want to dump it in the pool, there is already crust along the edge that is hard to get off. The softener helps but we sure do use alot of salt. Thanks for doing the arithmatic, that does make sense.

01/13/2009, 01:28 AM	#11
askolded Registered Member Join Date: Jan 2007 Location: The Jersey Shore Posts: 32	AZ....to answer your question about how I installed my filters: I just drained the whole system, removed the old cartridges , washed out the canisters and installed the 3 new cartridges plus a new RO membrane (did not change the resin). Then I started to run the system. Have I created any problems that can't be fixed?

01/13/2009, 05:07 AM	#12
Buckeye Hydro .Registered Member Join Date: Sep 2006 Location: Cincinnati, Ohio Posts: 4,857	Most vendors advise that you do something along the lines of what you did - but AZ is right. It is a better practice to flush each filter stage that needs it in order, installing the next after the previous is flushed so that you don't run "flush" water from one filter into the next filter. Russ