is a tds meter much use?

I've just got a ph meter which sounds like it will be helpful for checking my mash ph. I'm considering a tds meter for testing our water hardness but if it doesn't give me any information on the makeup of the dissolved solids is it going to be of much use? We're on tank water so I haven't got access to a water report.

A TDS (total dissolved solids) meter can be useful in a small number of cases. It can give the user an idea of the gross mineralization of the water supply, but with no indication of what ions it contains. If the TDS varies, the cause of the variation in the shift in TDS would have to be understood before any conclusion on water profile could be made. If the water company draws water from two or more starkly differing sources, the meter might help the user discern when this has occurred. If the water profiles from those sources were known, then the user might be able to guess what the current profile is. That's pretty iffy!

The other use that a TDS meter is well suited for is when using RO treatment. RO water from a properly operating unit should have a TDS of less than 10 ppm. In many cases, it can be less than 5 ppm. If the water presents a reading higher than this, it is an indication that the unit is failing and the assumption of nearly ion-free water cannot be used. Its then time to fix the unit or find another source (assuming the RO is purchased from a vending machine).

A handheld TDS meter has been handy to know how good my grocery store RO unit is working when buying brewing water. My city water is about 400ppm TDS and the grocery store water is consistently <25 ppm, usually about 15 ppm. So far I would have been fine without the meter, but it's a $20 tool to eliminate a variable.

http://www.tdsmeter.com/products/tds3.html

I lent it to a co-worker too who was curious about his city water TDS and ended up finding a plumbing issue with his refrigerator water dispenser that showed TDS the same as his softened water.

mabrungard said:

RO water from a properly operating unit should have a TDS of less than 10 ppm.

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I agree in part, but that's not completely true. We would all like to have our RO put out lower than 10ppmTDS, but most don't. I try to explain to customer's why I can get their RO to produce twice as good as they can all the time. Some listen, but sadly most don't.

The rule we generally go by is percentage. We want the RO rejection to be 85% or better(90% for rental customers.) Usually, you can get a quality RO to run at 90+% for 10+years. A lot of times the lower end "box store" units will give you 90+% for only a couple of years.

In short, if your supply water to the RO is 400ppmTDS we strive for a maximum of 40-50ppmTDS from the RO. A little higher isn't a big deal, but still the lower the better.

In closing; my supply to my RO is 360-500ppmTDS. My RO has ran at 10ppmTDS or lower for over 13 years. (Just showing that you CAN get a quality RO to produce great RO water for much longer than most people think or say.)

I have to agree that TDS < 10 from feed with a TDS of 500 would be impressive indeed - average rejection of 98%. Keep in mind that some ions are rejected more than others so what you get depends not only on the TDS but on the composition of it. The real value of TDS with respect to RO systems is in looking for and noting change. The meter in my unit has two probes - one in the feed stream and one in the permeate stream. If I see permeate TDS increase I can push the button and check feed TDS to see if that's the cause. If it isn't then I'd better have a look. I installed a Hobbs hour meter in the system and so am able to record TDS against hours in the log and would be able to detect a trend. This system has been in service about 2 yrs now and output TDS has remained less than 5 (touch wood). I used a couple of the cheapie GE units from Home Depot for 5 or more years without problems. I try to take care of my membranes which doesn't require that I do much except feed them with softened water. My silica runs about 28 mg/L and that concerns me but it hasn't gummed up (or glassed over) a membrane yet (again touch wood).

Actually, maybe 98% isn't all that impressive after all. My system seems to produce 97% average rejection. I really need to get into it and calibrate those conductivity probes.

Yes - 90% rejection is pretty low. I suspect you might be sending your permeate to a pressure tank - which would explain the low rejection.

Russ

Best thing to do with an RO system is to run it! I've told people over the last 20 years that the best thing you can do to help your RO work correctly is to use it. (Within reason.) The best thing you can do with an RO system is run it often. Drain it weekly to get more "cleaning" on your membrane. Change filters often and use it, use it, use it.

Can't tell you how many times I've taken a "bad" RO and made it work correctly simply by getting some water running through it. A membrane can't clean itself if not enough water is running though it......

Would 1 gpm at 99% rejection work for you?

Hackwood said:

The rule we generally go by is percentage. We want the RO rejection to be 85% or better(90% for rental customers.) Usually, you can get a quality RO to run at 90+% for 10+years. A lot of times the lower end "box store" units will give you 90+% for only a couple of years.

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So, are you saying that once the rejection falls below 90% it is time to replace the filters and membrane?

For clarification and education, is the rejection rate a measure of is the percentage of TDS left of the source water? i.e. My tap water after a water softener and whole house carbon filter has a PPM right around 300. My RO water has a PPM of 17 (both measured with a cheap internet PPM meter). So do I have a 94% rejection rate (17/300 = 5.6%).

Given this, I guess a person with an RO system needs to take a baseline PPM for your their system with fresh, broken in filters, and use that to help judge when to replace filters and the membrane.

From our FAQ's:
A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the usable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or more of the prefilters (all the filters that touch the water before it reaches the RO membrane) is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove much of the chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons. Remember that all the water you process, both waste water and purified water, goes through the carbon block.

Regarding your RO membrane and DI resin, use your total dissolved solids (TDS) meter to measure, record, and track the TDS (expressed in parts per million [ppm]) in three places: 1) tap water, 2) after the RO but before the DI, and 3) after the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 ppm. Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO membrane housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 96% (i.e., they reject 96% of the dissolved solids in the feed water). So the purified water coming from your 100 gpd membrane would be about 16 ppm (a 96% reduction). Filmtec 75 gpd (and below) membranes produce purified water (a.k.a. “permeate”) more slowly, but have a higher rejection rate (96 to 99%). The lifespan of an RO membrane is dependent upon how much water you run through it, and how “dirty” the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the TDS in the water coming into the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce purified water more slowly as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the TDS in the RO water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, your resin needs to be replaced. Sometimes you'll hear people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin high TDS water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal.

Additionally, don’t forget to sanitize the entire system at least once per year, and wash and lube your housing o-rings with food-grade silicone grease every filter change.

Russ

Buckeye_Hydro said:

From our FAQ's:
Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove much of the chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons. Remember that all the water you process, both waste water and purified water, goes through the carbon block.

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Be aware that carbon cartridges are often rated by the 'break-through time' for certain contaminants. Most of those contaminants are 'adsorbed' onto the carbon. However, chlorine compounds are not adsorbed onto the carbon, they react directly with the carbon and consume it. So the 2000 to 6000 gal ratings are likely for adsorbed contaminants. The 20000 gal rating is likely appropriate for chlorine compound destruction. So listen to Russ, you don't have to replace that filter too often.

The best way to assess carbon filter life is to monitor the Total Chlorine content in the post-filter flow. When you measure any chlorine in that flow, its time to replace the carbon filter immediately. A little chlorine compound reaching the RO membrane is OK for a short period of time.

In the case of typical municipal drinking water supplies, they are required by law to have really low sediment and particulate content. So its less likely that they will clog after passing several thousand gallons of water. I'm far less inclined to agree that a 6 month replacement interval is necessary. On a typical municipal water supply, you could easily see years of acceptable flow with a particulate filter. Monitoring the pressure drop across the filter when the RO unit is under full operation, is always the best way to assess filter clogging.

mabrungard said:

The other use that a TDS meter is well suited for is when using RO treatment. RO water from a properly operating unit should have a TDS of less than 10 ppm. In many cases, it can be less than 5 ppm. If the water presents a reading higher than this, it is an indication that the unit is failing and the assumption of nearly ion-free water cannot be used. Its then time to fix the unit or find another source (assuming the RO is purchased from a vending machine).

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This is exactly why I bought one. Typically with my system I get between 5 and 8 ppm, 6ppm being the most typical.

In my Buckeye system I'm getting about 4ppm in my permeate, with feed water typically around 200-250ppm. Better than 98% rejection. It's been a good $140 investment, and I was never comfortable with the dubious quality of the water from those grocery store machines. Plus, no more lugging containers to/from the store.

What system is that, I am all of a sudden curious.

Also be aware that when manufacturers state a "chlorine capacity" it is the number of treated gallons at which 50% of the chlorine passes. So although "chlorine capacity" is a somewhat standardized metric by which to compare carbon filters, don't assume it is the appropriate number of gallons that should pass before you change the filter.

mabrungard said:

However, chlorine compounds are not adsorbed onto the carbon, they react directly with the carbon and consume it.

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In the case of chlorine (Cl2 + H2O --> HCl + HOCl)

C* + HOCl --> CO* + H+ + Cl-

in which C* represents activated carbon and CO* the surface monoxide thereof. So indeed the chlorine oxidizes the activated carbon rendering it unable to reduce further chlorine.


Chloramine also oxidizes C*

C* + NH2Cl + H2O --> CO* + NH4+ + Cl-

but CO* is able to oxidize chloramine thereby being reduced back to C*. Once some of the surface oxide is formed

2NH2Cl + CO* --> N2 + C* + 2H+ + 2Cl- + H2O

Combining the two reactions we have for the steady state

3NH2Cl --> N2 + NH4+ + 3Cl- + 2H+

and the carbon isn't consumed at all!

Well that's the theory anyway. My question to the guys that sell, recommend, review, install, test.... activated carbon filters is "Is this what happens with chloramine in practice?"

Well, it would be nice if the carbon wasn't consumed in that reaction. But unfortunately those reactions don't tell the whole story.

Komorita and Snoeyink (1985) (who pioneered the analysis of these chlorine/activated carbon reactions), found that the two reactions do not proceed at the same rate. The second chloramine reaction shown above, proceeds at a much slower rate. The researchers also found that these reaction rates plateau. In addition, the reaction of chlorine compounds result in the production of total organic halides (TOX) that do end up entering the flow stream. So the materials that you're hoping to reconstitute into carbon, are lost to the flow.

The other thing that isn't considered in the equations above, is that chloraminated water does not exist solely as monochloramine. There is often a bit of dichloramine in the water. Dichloramine does consume the carbon.

My experience is that salesmen and installers are less likely to be aware of this chemistry. But they would tell you that carbon filters are consumed and must be replaced.

Interesting. Thanks!

mabrungard said:

So the 2000 to 6000 gal ratings are likely for adsorbed contaminants. The 20000 gal rating is likely appropriate for chlorine compound destruction. So listen to Russ, you don't have to replace that filter too often.

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Those numbers are all for chlorine capacity. To complicate the issue, there are only some manufacturers that do the chlorine capacity tests as they are supposed to be done (NSF/ANSI).

This has been an interesting thread. Thanks for the education. Having great water chemistry experts like you guys so open to helping the rest of us is really, really great. The formulas are over my head, but I think I am learning.


With all of the chlorine discussion, I am a bit confused and left wondering if there is chlorine and chloramine left after RO treatment, when it is working properly. Is it still significant enough to worry about when brewing? Should we still add campden tablets? As I mentioned previously I have a whole house carbon filter after my water softener. It is your basic clear Omni Filter canister with a Dupont carbon filter that I change every 6-10 months (there are only two of us in the house). I have a Costway 5 stage RO system with a booster pump and storage tank (PP-GAC-CTO-pump-RO-T33-tank). Should the CTO filter before the membrane and the T33 filter after it eliminate any chlorine left after my whole house filter?. I sometimes go 50%-RO/50% tap water to brew.

Thanks.

A properly engineered RO system should be producing chlorine/chloramine free water.

The whole house carbon filter could easily be overwhelmed if the flowrate is too high. A hose bib can easily flow at 5 gpm and that is likely to overwhelm the treatment capacity of the filter. Chlorine/chloramines would likely be present in the tap water, in that case.

applescrap said:

What system is that, I am all of a sudden curious.

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I bought the "Premium RO" system from Buckeye. I opted for the 75GPD, which is plenty fast for what I am using it for. I connected it to a hose bib above my laundry sink.

mabrungard said:

A properly engineered RO system should be producing chlorine/chloramine free water.

The whole house carbon filter could easily be overwhelmed if the flowrate is too high. A hose bib can easily flow at 5 gpm and that is likely to overwhelm the treatment capacity of the filter. Chlorine/chloramines would likely be present in the tap water, in that case.

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Agreed. Cartridge filters are really not a good choice if what you're trying to do is whole-house dechlorination. They are an even worse choice if you're looking for whole-house de-chloramination. A carbon tank is a better fit for whole-house treatment like this.

If you're using a carbon block - the largest of the four standard cartridge sizes is 20" x 4.5". They are typically rated for chlorine removal at a max flow of 5 to 7.5 gpm, but keeping flows at about half that or less is good practice. I'm not a huge fan of whole-house removal of the disinfectant. It's in there for an important purpose.

Russ

MaxStout said:

I bought the "Premium RO" system from Buckeye. I opted for the 75GPD, which is plenty fast for what I am using it for.

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Although a 75 gpd output may seem like it is much more than most home brewers need, remember:
1) if you feed the system water at less than 77F and or less than 50 psi, production will slow. For example, at 50F and 45 psi, you'll get only 39 gpd from a 75 gpd membrane.
2) even if you have the 50 psi and 77F, 75 gallons per day is only about 3.1 gallons per hour - these systems produce pure water slowly.
3) the cost difference in jumping from a 24 gpd, to a 36 gpd, to 50, 75, 100, or 150 gpd is very minimal - you're only talking about a few dollars difference.
4) Buckeye's membranes rated at 24 to 100 gpd are all factory spec'ed at 50 psi and 77F. The 150 gpd and the 200 gpd membranes are factory spec'ed at 65 psi and 77F.

Russ

Buckeye_Hydro said:

Although a 75 gpd output may seem like it is much more than most home brewers need, remember:
1) if you feed the system water at less than 77F and or less than 50 psi, production will slow. For example, at 50F and 45 psi, you'll get only 39 gpd from a 75 gpd membrane.
2) even if you have the 50 psi and 77F, 75 gallons per day is only about 3.1 gallons per hour - these systems produce pure water slowly.
3) the cost difference in jumping from a 24 gpd, to a 36 gpd, to 50, 75, 100, or 150 gpd is very minimal - you're only talking about a few dollars difference.
4) membranes rated at 24 to 100 gpd are all factory spec'ed at 50 psi and 77F. The 150 gpd and the 200 gpd membranes are factory spec'ed at 65 psi and 77F.

Russ

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That's been my experience. My tap water temp is in the low 50s, and I get about 2 gal/hour at best. That's just physics--colder water has a higher viscosity. Even in summer, my tap water will never reach 77F, as it's Minnesota and our mains are buried 8 feet deep. I think I get ~2.5 GPH in summer. My water pressure is good, usually 60 PSI or better.

I didn't know about 4), that the higher rate filters are spec'ed at higher pressure.

This leads me to a question: When it comes time for me to replace my filters, can I upgrade with 150 or 200 GPD filters and retrofit them into my system?

Those numbers apply to Buckeye's membranes only - I should have specified that above. Most membranes out there on the market are spec'ed at 65 psi.

Yes - you can change your membrane if you'd like - if you do, also consider changing your flow restrictor ($4) to something that will give you a reasonable concentrate to permeate ratio.

Russ

Buckeye_Hydro said:

I'm not a huge fan of whole-house removal of the disinfectant. It's in there for an important purpose.

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Isn't that the truth. While we may not like the chloriney flavor and aroma, the hazards of removing that disinfectant from our water supply can be deadly. There are several verified cases where carbon prefilters ended up creating hazardous conditions. For example, the original Legionaire's Disease outbreak was traced back to the hotel which installed a big carbon filter on their water supply and those Legionaire bacteria built up in the showerheads where they were ejected in an aerosol that infected the guest's lungs.

Whole house is a very bad idea.

Easy enough to remove at point of use.

From my salt water aquarium days - if you are having trouble with your RO membrane spitting out too high of TDS (most amazon systems come with crap membranes), order a DOW FilmTec membrane and be amazed at the TDS drop!