Water Report Unbalanced

[thekraken]

I'm trying to get a handle on my water report. When I input the report's data into Bru'n Water the spreadsheet is telling me that my "Water Report is unbalanced" and I should question the reported concentrations.

I'm using the Nov '14 report on the second to last page of the PDF linked above, and the "Treated" column. That report shows zero for HCO3 and CO3, using the spreadsheet calculator from reported CaCO3 and pH I estimated HCO3 and CO3 and plugged those into the input fields. With or without that I still get unbalanced results.

Can I trust my water reports? Am I inputting the data correctly? Also, just based on that report, how does my water profile look?

(edit) If I go back one month to the oct report I get perfectly balanced results from bru'n water. Do these water reports just have errors from time to time?

 

[ajdelange]

They always have errors but sometimes the errors cancel each other better than at others and sometimes the errors are larger or smaller and sometimes the numbers for a given ion are taken from different samples. Also, in computing balance, it is necessary to determine the charge on bicarbonate and carbonate ions which are determined from the alkalinity and pH numbers for the sample and the process for computation is apparently shrouded in some mystery as few seem to know how to do it. In your case, for example, the bicarbonate (derived from the November report) would be 98.1 and the carbonate 0.6 mg/L each. The carbonate you estimated is right on, the bicarbonate off a small amount. This assumes that the lab did the alkalinity titration to 4.4. If they did it to 4.3 the numbers would be 97.2 and 0.6. Clearly where you are only given the alkalinity and pH the probability of some error (from lack of knowledge of the end point pH) is pretty high.

If you get a Ward Labs (or other lab's report) that is way out of whack (0.3 mEq/L or more) you can often go back to them and say 'hey, isn't this a little high' and they will (or at least Ward Labs often will) agree and rerun the test for you. I don't think that same conversation with your water authority will get you very far.

Ward Labs has fairly recently been educated on how to compute bicarbonate and carbonate so presumably their imbalances should be smaller than they used to be.

There isn't much you can do about an imbalanced report except try to get a better balanced one.

 

[mabrungard]

The water utility probably does not test all parameters from a single sample and its possible that the water quality varies with time. I see that this is from a surface water source and they use coagulants and acid to treat the water.

One other component that could influence the imbalance is the presence of silicate. That is another anion that would help boost the anion total and possibly bring the balance slightly closer. Silicates are more prevalent in arid regions and have been reported at concentrations as high as 100 ppm in freshwater. A high silicate concentration is not the case here, but the silicate would help the balance calculation.

I suggest reviewing several months data and surmise what the typical range of each major ion is and fabricate a profile from that information. That may provide a reasonable estimate of the water quality over time.

 

[ajdelange]

Anything that's not measured (such as strontium, copper, iron...) will, of course, contribute to imbalance but, except under unusual circumstances their amounts are small though, as with iron and aluminum, for example, the ions are triply charged. The good news with respect to silicate is that while it is fairly common it is rarely found at concentrations above 30 mg/L (I'm just lucky I guess at 28 mg/L) and it's pK is pretty high at around 8.6 so that unless one's pH is unrealistically high and he is one of those with an unusual concentration silicate won't be much of a factor. In OP's case pH is 8.2 and even with the 'maximum' of 30 mg/L silicate would only contribute 0.01 mEq/L alkalinity. Note, however, that this would have two effects on a calculation. First, that 0.01 mEq (half a ppm as CaCO3) has to be deducted from the measured alkalinity (as does phosphate ion charge) before carbonate and bicarbonate charges are computed and second, of course, it has to be entered into the cation charge tally.

But note that if one fails to separately measure silica and is, thus, unable to correct alkalinity for it, that the result is an apparent alkalinity that is higher than correct with an apparent bicarbonate charge that is higher. Thus negative charge not attributed to the unmeasured silica still appears in the cation column under bicarbonate. Not 1 for 1, of course, there is still error. Thus, without doing detailed calculations, it would seem that the error from ignoring silica is to some extent canceled.

In any case nominal silica charges are so small as to moot further discussion.