TDS Discrepancy? Issue with.....? Trying to figure this out!

I recently moved and have a new water source now which prompted me to send a sample to Ward Labs for analysis.

When I received the report, one thing that struck my attention was the "est TDS" value of 798 ppm. (EPA defines a max contamination level of 500 ppm!) This was somewhat alarming so I contacted the water department and they were equally surprised but had no real comment other than they would consult their own labs on the topic.

So, I ordered a second analysis from Ward Labs and this time, "est TDS" was lower at 624 but still above 500. **My Cation/Anion numbers were also out of balance by >1!

After buying two analysis kits I decided it would be cheaper to buy a TDS meter at this point. (HM TDS-3) Once I received it, I'm happy to see TDS values of ~224-244; much better that the >500 numbers reported by Ward Labs.

Is this normal for Ward Labs or is there a problem with their analysis? The unbalanced Cation/Anion numbers suggest the latter....

Curious to know what the water wizards on this forum have to say. If I've left out key info, please let me know...

I don't know that I qualify as a water wizard but here are a few comments...

Is there any chance that you have a water softener on your system?

Assuming not, then there are a few possibilities:
The problem was temporary, due to some issue with the water system.
You have an issue with your water supply pipe system that could be allowing contaminants into your drinking water. Do you irrigate with potable water?
There is an issue with your method of gathering the water samples, not very likely.

Having said all that, I'm not sure that I'd be comfortable with the results from your water testing apparatus. Contact your water dept again and tell them of your second test, ask them to look into it. I know several people in that field and they take their responsibility very seriously.

I have no softener on "my system" but the Water dept. did say that they blend softened water with well water.

The TDS meter is supposedly trustworthy according to several posts on this forum though I admit I've not calibrated it. Supposedly it comes from the factory per-calibrated. I know that doesn't mean I shouldn't check it...

Water samples were taken after allowing a flow for ~5 minutes.

I would contact Ward labs. I would tell them just what you included here. I would ask if they would retest a sample for free. Then take a sample and send half to Ward and use the other half to test using your test kit. At least at this point, you'd know if there was a discrepancy between your test kit and Ward. Maybe even ask how long until they expect to receive and test it, and wait to test until the estimated time they would be testing, just to keep everything controlled.

As a sanity check, I just tested again with the TDS meter and it's now back to 600. Making me crazy.... Guess I'll call the water department again on that and reach out to Ward Labs on the topic. Will use the unbalanced report as a plea for a retest.

Since you've got the meter you also might consider testing water from other sources in town. Work, public library, neighbors, other public buildings and businesses.

That's a great idea. Thanks for the input folks!

I'd also see if you can test some bottled water with a known TDS range. That might help you know if your meter is in the right ballpark. Which TDS meter do you have?

I have the TDS-3 by HM Digital

Just checked bottled water with my TDS-3 and it read ~24ppm. Then I checked my tap water and it read 631ppm. It's looking like Ward Labs and my meter are telling me the truth. So, at least this will help my conversation with the water department tomorrow!

Thanks again folks!

Nagorg said:

I have the TDS-3 by HM Digital

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That's a decent meter. I have the TDS-4, which basically adds Automatic Temperature Compensation. You'll want to make sure your water temps are in the right target range to get accurate readings, but otherwise you should be good to go.

But meanwhile, with TDS in the 600+ range, I would definitely look into getting a decent 4-5 stage under sink filter!

There's a possible clue in the response from your water company. That they're blending with softened water. Chances are that they're using deionizers for this task. This often leaves the water with a slightly positive charge that tricks your meter into a higher reading.

TDS meters work by measuring a charge across two probes. Air bubbles on one or both probes can lower the reading. These meters are designed to be most accurate at about 25C, 75F, even if they have ATC.

There's some other squirrely things that can skew the reading, like static electricity. Dried on mineral deposits can also change the reading. Apparently, larger samples are also more accurate according to HM.

Given that you've taken multiple measurements, it seems to go back to the water co treatment for softening the water.

Supposedly the TDS-3 also has ATC according to HM Digital. The TDS-4 is a more compact model though mine isn't huge.

So, should I expect softened water to read higher TDS levels?

Doh! You're right. I was thinking of a different model.

Yes, soft water just means most of the calcium and magnesium is stripped out. This can be done either by removing them or adding certain salts, or even lime, to the water. The ions bond to each other and are less likely to grab onto your skin, pipes, etc., making it easier on your pipes and better for your skin. The question is, what method are they using to soften the water? I would hope not the easiest salt-based method, because that can add a huge amount of sodium to your diet if you're drinking the tap water. Any way you shake it, though, they're adding a bunch of stuff to the water to soften it, which sounds like MAY be tripping up your TDS meter. Still not the best for drinking (and I assume making beer), however. I would filter.

TDS meters are not truly accurate in estimating the dissolved solids content since they are using conductivity to provide a correlation. The higher the TDS value, the greater the possibility of error. I wouldn't put any value in the TDS meter reading over the lab measurement. The lab has a much better way of calculating TDS.

The thing that is of highest concern is the imbalance of cations and anions. That is a pair of results that you want to be fairly close. However, there may be some other ions in that water that the lab isn't testing for and they are missing from the totals of either the cations or anions. Based on the discussion, it doesn't sound as if this tap water is well suited for brewing. By the way, the 500 ppm TDS max is only a guidance value. It is not a legal requirement.

There are water companies that use ion-exchange softening on a large scale basis to soften the water supply. My city is one of those. My sodium content can approach 250 ppm...not good for brewing. RO is a given fact for my brewing.

A TDS meter that we would buy for brewing, doesn't directly measure the mineral content. It measures conductance, then calculates the corresponding TDS level. Lower mineral water is less conductive, so the meter shows lower TDS.

Salt treatment softeners will replace each magnesium and calcium ion with two sodium ions. Although that's a higher TDS value, the cations & anions remain balanced.

Deionizer systems work differently. Water goes through two separate stages, first to remove cations then anions. Since each process is separate, the result can be an imbalance. Typically its balanced towards cations because, ironically, sodium doesn't bond with the resin very well.

In stage one, cations pass a medium high in H+. In stage two, the water passes a media rich in OH-, removing anions. The two then combine to produce (duh) H2O. The resins have to be recharged periodically just from use. However, some minerals can quickly deplete the cation side, usually iron. So, when the process is incomplete, cations rise and usually it's as excess sodium.

The TDS meter sees the cations as lower resistance and easier conductance. That tricks the meter into a false high reading. The same thing can happen from temperature, static electricity and from too small a sample. Typically a 2 oz sample, moving the probe a little to break magnetic alignment is sufficient to get a reliable reading.

I'm just now noticing an apparent correlation with higher TDS and higher sodium. So, I guess this is an indicator of a salt based softening method driving both values?

09/15/2015 - TDS = 798 ppm - Sodium, Na = 303 ppm - Cations/Anions = 13.4/13.8
10/05/2015 - TDS = 636ppm - Sodium, Na = 205 ppm - Cations/Anions = 9.6/10.8

mabrungard said:

My sodium content can approach 250 ppm...not good for brewing. RO is a given fact for my brewing.

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I have been diluting with 50% distilled and will certainly be looking into an RO system assuming I will just have to live with this water!

Wow!

200-300 ppm sodium? Mine is 43 and that's on the borderline for the styles I brew.