7 TDS city water -> RODI necessary?

Trever · Jul 7, 2020

Similar questions to this have been asked before but the answers I've read and what I've researched so far still leaves me puzzling a bit, and therefore, wondering what folks would say to my question directly.

I started making my first batch of water. (Yay!)

When I had the purge open for the first few minutes (per RODI unit instructions), I noticed that incoming water was 20-30 TDS on the LED display. Now that I'm filtering/making water with the purge closed, it's saying that incoming water is 7 TDS. Outgoing cleaned water is 0 TDS. This is a 4 stage BRS RODI unit, with the TDS meter correctly inserted into the flow. City water.

At 7 TDS, I'm wondering if I need to use this thing?

Wouldn't some sort of removal of residual city purification chemicals be sufficient- maybe even leave the water sit to evaporate the chlorine(s), like we do with the house plant water? Or some treatment that is "less than" full on RODI?

If I were to get the tap water tested and the "7" doesn't include anything obviously unacceptable in an aquarium (not that I would immediately know what such things are)... and if 7 is a stable TDS out of the tap, is RODI necessary in my present circumstance?

kapnkush608 · Jul 7, 2020

I don't see why you wouldn't just keep using it. Your filters should last forever lol

wphan · Jul 7, 2020

I’d personally still would use a Ro system. Provides some peace and mind.

homer1475 · Jul 7, 2020

I have very clean water(24TDS) out of the tap, I still use RO/DI only because my house is fed with copper pipes, and I have no idea what that 24 TDS is.

You have the unit, I would still use it, you filters will last a long time.

WVNed · Jul 7, 2020

If your BRS unit came plumbed like mine The TDS is reported after the membrane and after the DI stage. Your numbers are typical.

WIReefer · Jul 7, 2020

I would use it like stated above for peace of mind. I don’t like anything above 1

Trever · Jul 7, 2020

@WVNed hmmm... Ok. So you're saying while IN is not the same as OUT, IN isn't really what's coming from the tap?

Re the "use it anyways" camp... if there's "danger" in 7, of course. But if 7 TDS is "harmless", then I'd much rather park my unit for when we move to someplace where the TDS is higher and therefore RODI is necessary, and in the meantime, in our current location, get my water at 1000 times the speed and not send 2/3d's of it down the drain!

Potatohead · Jul 7, 2020

WVNed said:
If your BRS unit came plumbed like mine The TDS is reported after the membrane and after the DI stage. Your numbers are typical.

I think this is probably correct. My water is 13 TDS out of the tap but that is almost unheard of, 7 would be incredible.

Having 20 with the flush open and then 7 after would make sense too. Almost certainly your meter is reading after the membrane.

homer1475 · Jul 7, 2020

Get it tested and find out then. In the mean time, I would still use RO/DI.

Randy Holmes-Farley · Jul 7, 2020

Trever said:
Similar questions to this have been asked before but the answers I've read and what I've researched so far still leaves me puzzling a bit, and therefore, wondering what folks would say to my question directly.

I started making my first batch of water. (Yay!)

When I had the purge open for the first few minutes (per RODI unit instructions), I noticed that incoming water was 20-30 TDS on the LED display. Now that I'm filtering/making water with the purge closed, it's saying that incoming water is 7 TDS. Outgoing cleaned water is 0 TDS. This is a 4 stage BRS RODI unit, with the TDS meter correctly inserted into the flow. City water.

At 7 TDS, I'm wondering if I need to use this thing?

Wouldn't some sort of removal of residual city purification chemicals be sufficient- maybe even leave the water sit to evaporate the chlorine(s), like we do with the house plant water? Or some treatment that is "less than" full on RODI?

If I were to get the tap water tested and the "7" doesn't include anything obviously unacceptable in an aquarium (not that I would immediately know what such things are)... and if 7 is a stable TDS out of the tap, is RODI necessary in my present circumstance?

TDS is not a useful indication of the purity of the water for our purposes.

It is really most useful to know that an RO/DI is doing its job. Even 1 ppm TDS is too much if it is copper, for example, from your own pipes.

Trever · Jul 7, 2020

I submitted my question to BRS (they are local to me... so also thought they might know the skinny on the local water around here). They just now responded:

"That is the TDS reading into the membrane, after the sediment and carbon filter. You really want to use 0 TDS water, so we would recommend keeping it. "

So @WVNed and @Potatohead you were correct.

Re @Randy Holmes-Farley , IIRC, the TDS was higher initially when I was using a combination of hot and cold water. With just cold it dropped to 7 (I think, don't really want to run down to experiment more just now). If what I'm reporting is accurate, and from what I've read about hot water heaters and various other theories, this might make sense, though apparently I don't fully understand yet how this is unit is plumbed and the consequences for TDS, including something like copper or what come out of a hot water tank versus the cold water run. I do know we don't have copper pipes- I can see all the plumbing in the ceiling downstairs from the point at which the water works enters the house.

Anyways, this is good. Tells me what I need to know. I don't feel (necessarily) stupid using this unit in our present house. Thanks all.

Trever · Jul 7, 2020

Hmmm... if my BRS "IN" TDS reading is post sediment and carbon filter, something like copper would probably still be in the water for the reading. I think.

KStatefan · Jul 7, 2020

Trever said:
@WVNed hmmm... Ok. So you're saying while IN is not the same as OUT, IN isn't really what's coming from the tap?

Re the "use it anyways" camp... if there's "danger" in 7, of course. But if 7 TDS is "harmless", then I'd much rather park my unit for when we move to someplace where the TDS is higher and therefore RODI is necessary, and in the meantime, in our current location, get my water at 1000 times the speed and not send 2/3d's of it down the drain!

With income water being 7 TDS you can change the flow restrictor to not use as much water. The membrane will last a long time as long as you keep up with changing the carbon filter.

Potatohead · Jul 7, 2020

Ok, we need to back the truck up here.

Either the BRS dude was wrong, or you misunderstood him.

The TDS going into the membrane is the same as coming out the tap (basically). The sediment filter and carbon are there to grab actual particles in the water, and chlorine, they do not reduce TDS and exist only to protect the membrane.

I still suspect (like Ned) the meter is reading after membrane and then again after DI. This is the way most are set up. It's easy enough to figure out by looking at the plumbing.

WVNed · Jul 7, 2020

I added a second dual read TDS to my filter. 124 in, 122 after first 2 stages, 2-5 after the membrane and 0 out. The first 2 stages have very little effect on TDS.

Adamantium · Jul 7, 2020

Take a look at where your TDS meters are plumbed in. Is the first one before the RO membrane, or after? That'll solve this.

You could also buy a $10 TDS meter from Amazon, or perhaps pull one of the meters out of the plumbing and dunking it in a glass of tap water to find out for sure what your tap TDS is.

Spieg · Jul 7, 2020

Municipal water supply can change quite a bit from season to season. I'd keep the RODI because you just never know what the treatment plant is doing on a given day.

As for TDS meters - 2 sensor units usually read the water coming out of the RO membrane and again coming out of the DI chamber(s)... A 3 sensor TDS meter will typically add a sensor before the RO membrane.

Trever · Jul 7, 2020

@Potatohead and @Adamantium the first TDS is indeed after the membrane. So I quoted the BRS guy exactly and if I understand what he was trying to say, what he said isn't correct.

Now I'm trying to understand what the flush valve is doing exactly and what the TDS reading is telling me when the flush valve is open... it's not obvious because naively, it LOOKS like if I close the flush valve, I should have no waste water coming out, which is not the case. Google...

Anyways- obviously I don't have 7 TDS coming out the tap! So the premise of this thread isn't accurate. I'll price a TDS meter out (one that isn't cr*p), and depending, measure our tap water out of curiosity and have yet-another-measuring-device on hand. I do know that I can't unplug the TDS meter on the RODI unit and dunk it in water for an accurate reading- saw a BRS video about that, that's not the way the TDS meter on the unit works (requires water flowing thru perpendicular to the probes).

But without a reading, I dunno if I have a high TDS such that no questions asked, use the RODI, or if I have a low one, but the advice here combined with everything else I've read makes sense to me- use the RODI.

What I should really price out is another membrane... upgrade to half the waste water, etc.

Lurned somethin' today. Just wish I hadn't flattened our neighbors roses when I backed that truck up....

Potatohead · Jul 7, 2020

Can you please link on BRS' site which system you have. There are a couple different types of flush valve.

Edit - It looks like the four stages come with a membrane flush valve...

Ok so what that is doing is bypassing the flow restrictor. So in other words it is allowing water to go unpressurized through the membrane to flush it out of contaminants. You only really need to do that maybe once a month. When you close it the flow restrictor comes back into play and the pressure will build again, and the membrane will become functional again. So the reason the TDS is higher with it opened up is because the membrane isn't doing nearly as much work.