RODI waste question

Mz. Fix It · Mar 2, 2021

Ok, so I know some of you reading this will gasp at my thoughts....but I have to ask/discuss anyway because it's truly bugging me not finding a good answer.

I have had a 4 stage "plus" RODI system from BRS for a little over 3 years. With the "plus" I am supposed to be getting more water than the standard 4 stage, but whatever. For the past few years I have paid my increased water bill due to the fact that for every 1 gallon of RODI water I successfully get, I lose 1 to 1.5 gallons as "waste" water. When I started my system up each time I used to set the valve to go out the waste only and wait for that to show "0" TDS output then I would turn it over to go into my storage bin with "0" TDS as well because that was the way I was instructed to do it. It took me about a year of wasting a lot of water to realize I didn't really have to do that initial step of turning it all to waste first and started running it into the storage bin upon turning the system on. I found that the "in" for the storage container was starting out at "0" TDS anyway so I no longer wanted to waste that initial water in the beginning.

A couple of months ago I called BRS because I had an aha moment and I wanted clarification. In my pea brain the way I see it, just like with water filters and purifiers for human consumption drinking water, once the water goes through the filter it is then "clean" and acceptable to use and there is no "waste" water that gets poured out. So I asked the rep why there is waste water on the RODI systems if in theory the water is "clean" after it has passed through the filters. His explanation was that the water that goes out through the waste line is filled with all the bad stuff one wants to rid themselves of, or in our cases rid our fish of, and only the good RODI water goes forward into the storage bin. I suppose that would not be so bad for a small amount of water usage, however, I have an aquarium room with several large tanks (I do both fresh and salt tanks) and I have been sending a little over 200 gallons of "waste" water down my driveway every week now for the past few years, hence the high water bills.

Because I still couldn't wrap my little pea brain around the BRS explanation I decided to do an experiment for myself. Over the past two weeks I have ran the "waste" water line into buckets and the RODI "good" line into my normal storage tank. I have used my TDS meter to test each bucket of "waste" water and have found that just as I suspected they are reading "0" TDS on the meter as well with only a small exception of the 1st bit of run off when I start things up I might get a small reading of 6 to 16 depending on how much is in that bucket.

So my question for discussion and hopefully get some clarification for myself is why is there "bad runoff water" if it tests out to be zero TDS? Isn't that what it's supposed to be? Is there something in that waste water one should be concerned about that will not show up on the TDS meter? I am feeling like I may start to run all my water into my storage bin, both "waste" and "good" lines and perhaps as an added safety measure pour a little Seachem Prime in there "just in case." When I started my first salt tank I used tap water and used Prime when mixing my salt water and never really had any issues....but I got caught up in the fact that everyone kept saying "you have to do that for salt tanks" so I gave in and bought my RODI system. I now use the RODI water for both my fresh and salt tanks. I am just struggling with all this "waste" water from the RODI system getting flushed out even when it's testing out to be zero TDS.

Any feedback? Theories? Concerns? Explanations?

Garf · Mar 2, 2021

The waste line goes to drain and will have a slightly increase TDS from you supply water (try measuring both). You should have a “T” valve which you open each time you run the unit until the TDS creep is discarded. This T valve is situated between the RO membrane and your DI resin. You then close this valve to send the water from the RO membrane through the DI resin, producing the cleanest water, usually a TDS of 1 or 2 maximum.

flyawaybirdie62 · Mar 2, 2021

Hmmm my first thought is that it could be your TDS meter and once it's over a certain point it just shows zero? Like how nitrates that are super high can show up as zero on an API test (when you dilute the high nitrate water the test then shows a ton of nitrates). Maybe try diluting the water water with the actual zero TDS water and see how it tests?

Just a thought

PBnJOnWheat · Mar 2, 2021

Mz. Fix It said:
Ok, so I know some of you reading this will gasp at my thoughts....but I have to ask/discuss anyway because it's truly bugging me not finding a good answer.

I have had a 4 stage "plus" RODI system from BRS for a little over 3 years. With the "plus" I am supposed to be getting more water than the standard 4 stage, but whatever. For the past few years I have paid my increased water bill due to the fact that for every 1 gallon of RODI water I successfully get, I lose 1 to 1.5 gallons as "waste" water. When I started my system up each time I used to set the valve to go out the waste only and wait for that to show "0" TDS output then I would turn it over to go into my storage bin with "0" TDS as well because that was the way I was instructed to do it. It took me about a year of wasting a lot of water to realize I didn't really have to do that initial step of turning it all to waste first and started running it into the storage bin upon turning the system on. I found that the "in" for the storage container was starting out at "0" TDS anyway so I no longer wanted to waste that initial water in the beginning.

A couple of months ago I called BRS because I had an aha moment and I wanted clarification. In my pea brain the way I see it, just like with water filters and purifiers for human consumption drinking water, once the water goes through the filter it is then "clean" and acceptable to use and there is no "waste" water that gets poured out. So I asked the rep why there is waste water on the RODI systems if in theory the water is "clean" after it has passed through the filters. His explanation was that the water that goes out through the waste line is filled with all the bad stuff one wants to rid themselves of, or in our cases rid our fish of, and only the good RODI water goes forward into the storage bin. I suppose that would not be so bad for a small amount of water usage, however, I have an aquarium room with several large tanks (I do both fresh and salt tanks) and I have been sending a little over 200 gallons of "waste" water down my driveway every week now for the past few years, hence the high water bills.

Because I still couldn't wrap my little pea brain around the BRS explanation I decided to do an experiment for myself. Over the past two weeks I have ran the "waste" water line into buckets and the RODI "good" line into my normal storage tank. I have used my TDS meter to test each bucket of "waste" water and have found that just as I suspected they are reading "0" TDS on the meter as well with only a small exception of the 1st bit of run off when I start things up I might get a small reading of 6 to 16 depending on how much is in that bucket.

So my question for discussion and hopefully get some clarification for myself is why is there "bad runoff water" if it tests out to be zero TDS? Isn't that what it's supposed to be? Is there something in that waste water one should be concerned about that will not show up on the TDS meter? I am feeling like I may start to run all my water into my storage bin, both "waste" and "good" lines and perhaps as an added safety measure pour a little Seachem Prime in there "just in case." When I started my first salt tank I used tap water and used Prime when mixing my salt water and never really had any issues....but I got caught up in the fact that everyone kept saying "you have to do that for salt tanks" so I gave in and bought my RODI system. I now use the RODI water for both my fresh and salt tanks. I am just struggling with all this "waste" water from the RODI system getting flushed out even when it's testing out to be zero TDS.

Any feedback? Theories? Concerns? Explanations?

From the limited knowledge I know. TDS is Total dissolved solids. It essentially works by sending a current through the sample and measuring the particles. This works for electrically charged particles which are most. However, some compounds and solutions can contain uncharged particles. These are not measured in a standard TDS meter. This is because they do not reciprocate the electrical current through the sample.

Gtinnel · Mar 2, 2021

I don't have much to add other than the impurities in the water get stopped by the membrane and then the waste water rinses the impurities away from the outside of the membrane, or at least that is how it theoretically works. I've never actually measured the tds of my waste water though.

missourimud · Mar 2, 2021

just trying to follow along as I don’t like “wasting” water either.
so does waste water and clean both pass through the membrane? And as such like gtinnel said is it only really “dirty” water when we flush the membrane?

ExoS · Mar 2, 2021

The RO is a separation process. So of all the solids that go in, nearly 100% are diverted to waste. So now you can see its just math. If I have 100 ppm of solids coming in and I recover half my water as permeate, then the exit stream concentration must have doubled and it will be 200 ppm.

ROs are not a particulate removal. Its not like a filter that traps solids. It works strictly by diversion (or you scale the whole thing up which means it won't work anymore). So your TDS cannot be 0 in the waste stream. The solids have to go somewhere. I would check your meter. It seems its not right.

Gtinnel · Mar 2, 2021

missourimud said:
just trying to follow along as I don’t like “wasting” water either.
so does waste water and clean both pass through the membrane? And as such like gtinnel said is it only really “dirty” water when we flush the membrane?

Only the good water passes through the membrane. The waste water goes on the outside of the membrane. The difference when flushing the membrane is that you remove the restriction in the waste line so the water quickly flows over the outside of the membrane to "clean" it.

the_cros · Mar 2, 2021

Can you at least use your waste water for your fresh water system (with some prime)? I bet it’s way cleaner than the tap water you used to use for them.

Fish man · Mar 2, 2021

I've had some of the same questions, more so as it relates to operating pressure. When I researched RODI membranes they are rated by the manufacturer for minimum recommended operating pressure. I have a 75gpd Dow membrane with minimum recommended operating pressure of 50psi. Why then does that little valve on the waste line only put my RODI operating psi at about, I think it was 10psi or less. My home water pressure is 65psi. My theory is that most of the water is just bypassing the membrane and only going through the prefilters. You said your waste water is also 0 TDS. Could it be the prefilters are getting that result for you? Anyway, I put a shut off ball valve on the waste line and close it off until my RODI operating pressure is 50psi. This forces more water through the membrane and I get way way less waste water. More like 90/10. Set this way it produces the membrane rated output of 75gpd. I know this because I need 25 gallons for my water changes and ato refill in between. I set my timer for 8 hours and it consistently makes 25 gallons. My output water TDS is 0. I've never tested TDS on my waste water. I've done it like this for several years. With no adverse affects on my tank. My fish and corals are happy. I do however replace my membrane more often then is recommended. Again this is just my deduction but it works for me. ? Also don't tell anyone, it's my little secret.

Fish man · Mar 2, 2021

Mz. Fix It said:
Ok, so I know some of you reading this will gasp at my thoughts....but I have to ask/discuss anyway because it's truly bugging me not finding a good answer.

I have had a 4 stage "plus" RODI system from BRS for a little over 3 years. With the "plus" I am supposed to be getting more water than the standard 4 stage, but whatever. For the past few years I have paid my increased water bill due to the fact that for every 1 gallon of RODI water I successfully get, I lose 1 to 1.5 gallons as "waste" water. When I started my system up each time I used to set the valve to go out the waste only and wait for that to show "0" TDS output then I would turn it over to go into my storage bin with "0" TDS as well because that was the way I was instructed to do it. It took me about a year of wasting a lot of water to realize I didn't really have to do that initial step of turning it all to waste first and started running it into the storage bin upon turning the system on. I found that the "in" for the storage container was starting out at "0" TDS anyway so I no longer wanted to waste that initial water in the beginning.

A couple of months ago I called BRS because I had an aha moment and I wanted clarification. In my pea brain the way I see it, just like with water filters and purifiers for human consumption drinking water, once the water goes through the filter it is then "clean" and acceptable to use and there is no "waste" water that gets poured out. So I asked the rep why there is waste water on the RODI systems if in theory the water is "clean" after it has passed through the filters. His explanation was that the water that goes out through the waste line is filled with all the bad stuff one wants to rid themselves of, or in our cases rid our fish of, and only the good RODI water goes forward into the storage bin. I suppose that would not be so bad for a small amount of water usage, however, I have an aquarium room with several large tanks (I do both fresh and salt tanks) and I have been sending a little over 200 gallons of "waste" water down my driveway every week now for the past few years, hence the high water bills.

Because I still couldn't wrap my little pea brain around the BRS explanation I decided to do an experiment for myself. Over the past two weeks I have ran the "waste" water line into buckets and the RODI "good" line into my normal storage tank. I have used my TDS meter to test each bucket of "waste" water and have found that just as I suspected they are reading "0" TDS on the meter as well with only a small exception of the 1st bit of run off when I start things up I might get a small reading of 6 to 16 depending on how much is in that bucket.

So my question for discussion and hopefully get some clarification for myself is why is there "bad runoff water" if it tests out to be zero TDS? Isn't that what it's supposed to be? Is there something in that waste water one should be concerned about that will not show up on the TDS meter? I am feeling like I may start to run all my water into my storage bin, both "waste" and "good" lines and perhaps as an added safety measure pour a little Seachem Prime in there "just in case." When I started my first salt tank I used tap water and used Prime when mixing my salt water and never really had any issues....but I got caught up in the fact that everyone kept saying "you have to do that for salt tanks" so I gave in and bought my RODI system. I now use the RODI water for both my fresh and salt tanks. I am just struggling with all this "waste" water from the RODI system getting flushed out even when it's testing out to be zero TDS.

Any feedback? Theories? Concerns? Explanations?

I've had some of the same questions, more so as it relates to operating pressure. When I researched RODI membranes they are rated by the manufacturer for minimum recommended operating pressure. I have a 75gpd Dow membrane with minimum recommended operating pressure of 50psi. Why then does that little valve on the waste line only put my RODI operating psi at about, I think it was 10psi or less. My home water pressure is 65psi. My theory is that most of the water is just bypassing the membrane and only going through the prefilters. You said your waste water is also 0 TDS. Could it be the prefilters are getting that result for you? Anyway, I put a shut off ball valve on the waste line and close it off until my RODI operating pressure is 50psi. This forces more water through the membrane and I get way way less waste water. More like 90/10. Set this way it produces the membrane rated output of 75gpd. I know this because I need 25 gallons for my water changes and ato refill in between. I set my timer for 8 hours and it consistently makes 25 gallons. This makes me think it's operating as the manufacture recommends. My output water TDS is 0. I've never tested TDS on my waste water. I've done it like this for several years. With no adverse affects on my tank. My fish and corals are happy. I do however replace my membrane more often then is recommended. Again this is just my deduction but it works for me. ? Also don't tell anyone, it's my little secret.

ReeferLou · Mar 2, 2021

I collect all my "waste water" and use it to wash clothes. I would never send it down the drain but i'm cheap that way.

Garf · Mar 2, 2021

Fish man said:
I've had some of the same questions, more so as it relates to operating pressure. When I researched RODI membranes they are rated by the manufacturer for minimum recommended operating pressure. I have a 75gpd Dow membrane with minimum recommended operating pressure of 50psi. Why then does that little valve on the waste line only put my RODI operating psi at about, I think it was 10psi or less. My home water pressure is 65psi. My theory is that most of the water is just bypassing the membrane and only going through the prefilters. You said your waste water is also 0 TDS. Could it be the prefilters are getting that result for you? Anyway, I put a shut off ball valve on the waste line and close it off until my RODI operating pressure is 50psi. This forces more water through the membrane and I get way way less waste water. More like 90/10. Set this way it produces the membrane rated output of 75gpd. I know this because I need 25 gallons for my water changes and ato refill in between. I set my timer for 8 hours and it consistently makes 25 gallons. My output water TDS is 0. I've never tested TDS on my waste water. I've done it like this for several years. With no adverse affects on my tank. My fish and corals are happy. I do however replace my membrane more often then is recommended. Again this is just my deduction but it works for me. ? Also don't tell anyone, it's my little secret.

You’re trashing your membrane prematurely, and your DI.

albano · Mar 2, 2021

Seems like something is wrong... the waste water should not be 0TDS.

I can tell you that for the past 20 years, I’ve been using the waste water for my indoor and some outdoor plants, and there’re all doing great.

thewire · Mar 2, 2021

This is why i m making water the day I am doing laundry!

Fish man · Mar 2, 2021

Garf said:
You’re trashing your membrane prematurely, and your DI.

Perhaps but I'm not seeing that. I'm running it at the manufactures recommended pressure and getting the rated output. My TDS output remains at zero for a couple of years before I have to replace my membrane and I replace my DI when it changes color. Even so, I feel like a more frequent membrane replacement is cheaper then running a few thousand gallons of water down the drain a year.

Speaker · Mar 2, 2021

ReeferLou said:
I collect all my "waste water" and use it to wash clothes. I would never send it down the drain but i'm cheap that way.

I used to do this, but after overflowing the washing machine a couple times and angering my wife I decided it wasn't worth it.

ReeferLou · Mar 2, 2021

Speaker said:
I used to do this, but after overflowing the washing machine a couple times and angering my wife I decided it wasn't worth it.

I can see that. i collect in a tote in basement that has a drain and haul it upstairs 10 g at a time (my exercise) . So no big deal if it overflows. FYI - you can bucket flush your toilets too.

mdb_talon · Mar 2, 2021

It sounds to me like there is something wrong with your process or your TDS meter. As for just using both the good and waste and tossing in some Seachem Prime that is nonsensical. I mean if you want to use the wastewater that is your choice, but no point for using prime unless you dont use a carbon filter on your RODI(even then in a saltwater tank chlorine and even chloramines get broke down extremely quickly). However if you are going to use both good and waste water then might as well eliminate the whole RO portion of your RODI. Just run through prefilter and carbon. DI portion could still do something, but will go bad quickly if not going through RO first.