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Extra RODI Water


Wizzy

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It is my understanding that an RODI unit must be used at least every couple weeks (14-15 days or so) to keep the membrane wet and you have to make 10+ gallons to keep a good waste water ratio.

 

I only have a small nano though and don't do water changes but once a month.

 

As a result I always end up having extra water that I usually just throw away.

 

Is there something else I can use my water for?

 

Do I need to make so much so often?

 

Ideas to reduce the amount of water I am wasting?

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It costs like $0.30. Just throw it away.

 

That's what I've been doing, but I don't think there's anything wrong with asking.

 

Disconnect the DI portion and just make RO water for drinking.

 

I'll look into how to do that, but I don't think I want to mess with my unit.

 

Thanks- Wizzy

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As Mike said, use it for drinking water. We spend a fortune on little plastic bottle of drinking water when you have the answer at your fingertips. Install a tee and ball valve between the RO membrane and DI filter and enjoy good tasting safe drinking water. We have used RO in our home for over 15 years now as well as RO/DI for the tanks.

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BuckeyeFieldSupply

Back to the original post:

1. You should use the system at least once per week, rather than once per two weeks.

2. The amount of water you make each time has nothing to do with the ratio of waste water to purified water. Realize that everytime an RO system kicks on, you get about a minute's worth of not so clean water out of it (caused by "TDS creep"). So by leaving an RO system on for an extended period of time, you dilute that TDS creep water with lots of 0 TDS water. If you only run the system for a couple of minutes, 50% of the produced water will contain a high TDS.

 

The idea re using your system for drinking water is a good one. You could even hook up a pressure tank and faucet on your kitchen sink - but be careful if you do this. You have to plumb it coorectly so that RO water from the pressure tank never reaches the DI stage. It's easy to do.

 

The other thought I had is that you could get a slower membrane. Something like a 24 gpd membrane. That way you can use it more often but when you do it doesn't produce so much water. If you change to a slower membrane make sure you change your flow restrictor as well.

 

Russ

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+1 for drinking ! :D

 

We have a small pressure tank (one way valve before it, so it can't backflow as BFS said) and it goes to our fridge. We have guests that comment on the water all the time... "wow this water is so good, it tastes like clouds"

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As Mike said, use it for drinking water. We spend a fortune on little plastic bottle of drinking water when you have the answer at your fingertips. Install a tee and ball valve between the RO membrane and DI filter and enjoy good tasting safe drinking water. We have used RO in our home for over 15 years now as well as RO/DI for the tanks.

 

Thanks, I may end up doing this :happy:

 

Back to the original post:

1. You should use the system at least once per week, rather than once per two weeks.

2. The amount of water you make each time has nothing to do with the ratio of waste water to purified water. Realize that everytime an RO system kicks on, you get about a minute's worth of not so clean water out of it (caused by "TDS creep"). So by leaving an RO system on for an extended period of time, you dilute that TDS creep water with lots of 0 TDS water. If you only run the system for a couple of minutes, 50% of the produced water will contain a high TDS.

 

The idea re using your system for drinking water is a good one. You could even hook up a pressure tank and faucet on your kitchen sink - but be careful if you do this. You have to plumb it coorectly so that RO water from the pressure tank never reaches the DI stage. It's easy to do.

 

The other thought I had is that you could get a slower membrane. Something like a 24 gpd membrane. That way you can use it more often but when you do it doesn't produce so much water. If you change to a slower membrane make sure you change your flow restrictor as well.

 

Russ

 

So, you're basically saying that it isn't how much water I'm making it's the amount of time that the unit is being used? If that's the case, then how long do you recommend I run my unit every week? How many gallons would this be?

 

+1 for drinking ! :D

 

We have a small pressure tank (one way valve before it, so it can't backflow as BFS said) and it goes to our fridge. We have guests that comment on the water all the time... "wow this water is so good, it tastes like clouds"

 

Sounds yummy :D

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BuckeyeFieldSupply
So, you're basically saying that it isn't how much water I'm making it's the amount of time that the unit is being used? If that's the case, then how long do you recommend I run my unit every week?

There's not really a precise answer for your question w/o some additional data, but here is some guidance.

 

The duration of the "TDS Creep Period" - that time when higher than normal TDS can be measured in the water produced by your system, varies, and the actual TDS of that water varies. Here's some real data for instance:

 

TDSCreep.jpg

 

Using these data, and assuming your goal is to generate 0 ppm TDS water, it would take about 40 minutes of run time to produce a reservoir of water that would measure 0 ppm on your TDS meter on this example system.

 

The time necessary to do the same on your system would be different, and would be affected by the TDS of your feedwater, and your TDS creep profile (as shown in the graphlikelihood likelyhood you're probably talking about 30 minutes to an hour or more.

 

 

 

How many gallons would this be?

That would depend upon the production rate of your particular system.

 

Russ

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There's not really a precise answer for your question w/o some additional data, but here is some guidance.

 

The duration of the "TDS Creep Period" - that time when higher than normal TDS can be measured in the water produced by your system, varies, and the actual TDS of that water varies. Here's some real data for instance:

 

TDSCreep.jpg

 

Using these data, and assuming your goal is to generate 0 ppm TDS water, it would take about 40 minutes of run time to produce a reservoir of water that would measure 0 ppm on your TDS meter on this example system.

 

The time necessary to do the same on your system would be different, and would be affected by the TDS of your feedwater, and your TDS creep profile (as shown in the graphlikelihood likelyhood you're probably talking about 30 minutes to an hour or more.

 

 

 

 

That would depend upon the production rate of your particular system.

 

Russ

 

Thank you, but what are the stats/unit details for the chart you provided?

 

Time-Wise, I've been running my RODI approximately 3 hours every couple of weeks- Just FYI.

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The graph Russ provided should apply to any 25 to 75 GPD Dow Filmtec RO membrane. Every membrane is going to be slighly different as they are man made and each is unique. Overall though they will not vary significantly if they fall within factory specs. One problem though is most vendors with the exception of one or two do not test the membranes before delivery so its a case of you get what you get.

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The graph Russ provided should apply to any 25 to 75 GPD Dow Filmtec RO membrane. Every membrane is going to be slighly different as they are man made and each is unique. Overall though they will not vary significantly if they fall within factory specs. One problem though is most vendors with the exception of one or two do not test the membranes before delivery so its a case of you get what you get.

 

Well, my specific unit is a Spectrapure 90GPD and I think they test the unit before sending it out.

 

Any more advice concerning minimum water to make, now that you know the specific unit?

 

Thanks for all the help everyone- Wizzy :happy:

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BuckeyeFieldSupply
Well, my specific unit is a Spectrapure 90GPD and I think they test the unit before sending it out.

 

Any more advice concerning minimum water to make, now that you know the specific unit?

 

Thanks for all the help everyone- Wizzy :happy:

I'd stick with the advice above.

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Can someone explain to me why the RO system that I've been running for years has NEVER produced this so called "TDS Creep" that everyone talks about? I got very concerned about this years ago after reading about it and I still can't make my unit produce any TDS out of the DI end, regardless of how long it's sat. I've tried. I think about it on occasion and test for it and I aint gettin' it. :) I realize that there is a whole set of variables that change the results of this test, but I'm getting nothing and never have. Perhaps my TDS meter is bad and has been bad ever since I had it? My tap is ~130. Membrane output is 2-3. DI is 0. Whatup with 'dat. LOL

 

I'm not saying that it doesn't happen, but it doesn't happen to me and there seems to be an awful lot of information going around that may or may not be true for the masses.

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Can someone explain to me why the RO system that I've been running for years has NEVER produced this so called "TDS Creep" that everyone talks about? I got very concerned about this years ago after reading about it and I still can't make my unit produce any TDS out of the DI end, regardless of how long it's sat. I've tried. I think about it on occasion and test for it and I aint gettin' it. :) I realize that there is a whole set of variables that change the results of this test, but I'm getting nothing and never have. Perhaps my TDS meter is bad and has been bad ever since I had it? My tap is ~130. Membrane output is 2-3. DI is 0. Whatup with 'dat. LOL

 

I'm not saying that it doesn't happen, but it doesn't happen to me and there seems to be an awful lot of information going around that may or may not be true for the masses.

Measure the first amount of water coming from the RO membrane and you'll see the higher TDS than normal.

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godfathernikki
Can someone explain to me why the RO system that I've been running for years has NEVER produced this so called "TDS Creep" that everyone talks about? I got very concerned about this years ago after reading about it and I still can't make my unit produce any TDS out of the DI end, regardless of how long it's sat. I've tried. I think about it on occasion and test for it and I aint gettin' it. :) I realize that there is a whole set of variables that change the results of this test, but I'm getting nothing and never have. Perhaps my TDS meter is bad and has been bad ever since I had it? My tap is ~130. Membrane output is 2-3. DI is 0. Whatup with 'dat. LOL

 

I'm not saying that it doesn't happen, but it doesn't happen to me and there seems to be an awful lot of information going around that may or may not be true for the masses.

I'm not totally sure on this, but I think they are referring to water coming directly from the membrane. I would think that the DI resin could pull out the extra TDS.

 

EDIT: Jedi beat me to it :)

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I will test my water coming directly out of the membrane later to see what happens. I haven't ran it since yesterday morning. It's been a while since I've done it. My question is - do I run just a little squirt and test that? 4 oz? 8 oz? I mean, if it's the first 2-3 MLs that come out that's the problem, I'm not going to get an accurate reading once I get enough to test with my tester. I probably need at least 4 oz to run a test.

 

The reason I mentioned coming out of the DI is because the above statements reflect concerns, suggesting running the unit for several minutes before using the water that comes out. Even if there were a slightly elevated level of TDS into the DI, it would hardly be any concern to the point of needing to run the unit until you use the water. You might burn your resin up a micro-second faster that way though. :)

 

I think there may be some over-thought happening here. :) To the op - I would just run the unit when you need to run it and not concern yourself too much about ruining the membrane. As long as the system remains hooked up to a water supply, even when it isn't running your membrane is not going to dry out, get stale, or rot in any way. It is encapsulated in a water-filled container. The water remains in the system whether it is running or not.

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I'd stick with the advice above.

 

From AZ?

 

Does that mean I only need to run my RODI for a few minutes to get rid of TDS and prevent Creep as suggested in the quote below?

 

Why not just let the rodi drain into a bucket for the first 5min or so to get rid of the high tds water?
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BuckeyeFieldSupply
Thank you, but what are the stats/unit details for the chart you provided?

Each line in the graph represents a start up event using a 75 gpd system.

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EVERY membrane regardless of GPD, manufacturer or vendor suffers from TDS creep, it unavoidable.

 

What happens is when the system is shut down there is still tap water surrounding the membrane. The tap water contains TDS, the treated water on the other side of the membrane has been through the membrane and is low in TDS and at this point is somewhat agressive, trying to gain back the TDS or ions that have been stripped from it. Water does not like to be clean, it will do everything it can to get back to its natural "dirty" state. So, the tap water osmoses through the membrane contaminating or raising the TDS on the treated side of the membrane.

 

This is the first spurt of water that leaves the membrane when you first turn it back on again and will have this "TDS creep" until the treated water replaces the creep water. It happens to all systems.

 

The problem with TDS creep, although its a small amount of water in teh grand scheme of things, is it reduces the life of the DI resin since resin has a limited capacity to treat TDS. There are things you can do to reduce its effects though. Russ at Buckeye includes a bypass valve on his Premium series systems which you can use to manually flush the TDS creep to the drain for a minute or so then close the valve and the RO water passes on to the DI filter. The problem here is if you are like a lot of us and automate your system you may not be around to open the valve each time the system starts to replenish your ATO reservoir or your drinking water pressure tank. There are automated valves but they are pretty expensive at this point and the savings in DI replacements may not be enough to justify the expense.

 

I never get too concerned about TDS creep as it is only a few ounces of water but it is something you need to be aware of. To test the TDS creep you need the bypass valve between the RO and DI or you need to disconnect or remove the DI to test RO only. This is something I highly recommend doing anyway since the RO membrane is the workhorse of your system and you need to know your rejection rate or removal efficiency to troubleshoot the system. If its not removing say 95-98% of the TDS you are probably better off replacing the RO membrane with a new high rejection rate model as it will cut your DI resin costs drastically and quickly pay for itself. many people only sample the final RO/DI and have no idea if the RO membrane is working or not. ANY RO/DI should give you 0 TDS, at least for a little bit. Its how well the RO membrane is working that determines how good the system is though and you need to know that.

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BuckeyeFieldSupply
Before today, I never thought of water as being 'aggressive', but I learn so much from every post AZ makes. :lol:

 

DI water will corrode through copper pipes - so in general, no metal contact for DI water (some stainless steel is ok).

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  • 2 weeks later...
Each line in the graph represents a start up event using a 75 gpd system.

 

Thank you :happy:

 

EVERY membrane regardless of GPD, manufacturer or vendor suffers from TDS creep, it unavoidable.

 

What happens is when the system is shut down there is still tap water surrounding the membrane. The tap water contains TDS, the treated water on the other side of the membrane has been through the membrane and is low in TDS and at this point is somewhat agressive, trying to gain back the TDS or ions that have been stripped from it. Water does not like to be clean, it will do everything it can to get back to its natural "dirty" state. So, the tap water osmoses through the membrane contaminating or raising the TDS on the treated side of the membrane.

 

This is the first spurt of water that leaves the membrane when you first turn it back on again and will have this "TDS creep" until the treated water replaces the creep water. It happens to all systems.

 

The problem with TDS creep, although its a small amount of water in teh grand scheme of things, is it reduces the life of the DI resin since resin has a limited capacity to treat TDS. There are things you can do to reduce its effects though. Russ at Buckeye includes a bypass valve on his Premium series systems which you can use to manually flush the TDS creep to the drain for a minute or so then close the valve and the RO water passes on to the DI filter. The problem here is if you are like a lot of us and automate your system you may not be around to open the valve each time the system starts to replenish your ATO reservoir or your drinking water pressure tank. There are automated valves but they are pretty expensive at this point and the savings in DI replacements may not be enough to justify the expense.

 

I never get too concerned about TDS creep as it is only a few ounces of water but it is something you need to be aware of. To test the TDS creep you need the bypass valve between the RO and DI or you need to disconnect or remove the DI to test RO only. This is something I highly recommend doing anyway since the RO membrane is the workhorse of your system and you need to know your rejection rate or removal efficiency to troubleshoot the system. If its not removing say 95-98% of the TDS you are probably better off replacing the RO membrane with a new high rejection rate model as it will cut your DI resin costs drastically and quickly pay for itself. many people only sample the final RO/DI and have no idea if the RO membrane is working or not. ANY RO/DI should give you 0 TDS, at least for a little bit. Its how well the RO membrane is working that determines how good the system is though and you need to know that.

 

Thanks for the information, however I am still confused on the following-

 

If I did test my RO by removing the DI filter wouldn't that damage the RO membrane by making it work harder and expose it to Higher TDS water?

 

I always thought that I was supposed to be worried about TDS Creep in the RO Membrane, but it sounds like the DI Resin cartridge (before the membrane) is more important?

 

I am confused as to which cartridges I am supposed to remove or bypass to cleanse the system and why I couldn't cleanse the unit with everything setup the way it is?

 

If I'm unclear on anything LMK and sorry that I'm not understanding the information right away.

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BuckeyeFieldSupply
If I did test my RO by removing the DI filter wouldn't that damage the RO membrane by making it work harder and expose it to Higher TDS water?
Your RO membrane should touch the water before the DI
I am confused as to which cartridges I am supposed to remove or bypass to cleanse the system and why I couldn't cleanse the unit with everything setup the way it is?
When you say "cleanse"are you talking about when you sanitize the system once a year or when you flush the membrane?
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