Watertest: Any indicators for corrosivity?

[DetRack]

Hi,

I had a lab test my water at the faucet (behind the softener). It's city water, but not chlorinated - chlorination is only up to code as an intervention when a line breaks, not as a permanent measure by the municipality.

The lab advised me (unasked) to blend the water so I get around 6 GPG, otherwise I would have to deal with line damage.

I added my results, do you see anything that suggests corrosivity? I am confident in their analytical quality, but I have some doubts about the advice they give me.


Physical parameters:

pH-value at 61.7°F: 8.68
Conductivity: 549 uS/cm (limit: 2500)
Haze: 0.38 NTU (limit: 1.0)

Chemical parameters:
Hardness: 0.6 GPG
Acidic capacity: n/a
Hydrogen carbonate: 0 mg/l
Nitrate: 36.96 mg/l
Chloride: 43.2 mg/l
PO4 (phosphate): <0.05 mg/l
Ca: 2.7 mg/l
Potassium: 0.4 mg/l
Magnesia: 1.1 mg/l
Sodium: 109 mg/l (mostly from the softener, of course)
Strontium: 0.02 mg/l
Aluminum: <10 ug/l (too low to measure)
Arsenic: <8 ug/l (too low to measure)
Boric: 54 ug/l
Barium: 3.4 ug/l
Cadmium: <1 ug/l (too low to measure)
Chrome: <2 ug/l (too low...)
Copper: 3.2 ug/l
Iron: 4.8 ug/l
Manganese: 1.5 ug/l
Nickel: <2 ug/l (too low...)
Lead: <5 ug/l (too low...)
Uranium: <3 ug/l (too low to measure)
Zinc: 5 ug/l

For me, this does not look corrosive. The water has a moderately high pH, but nothing that should eat our pipes which are galvanized steel and partly copper. The galvanized steel is due for exchange in the next years, anyway, but that's going to happen section by section.

 

[Gsmith22]

look up Langelier index to discern how corrosive the water is https://www.lenntech.com/calculators/langelier/index/langelier.htm
you can get corrosive water even if pH is above 7 depending on water constituents.

 

[Sponsor]

 

[Reach4]

Ryzner is another, but it wants "alkalinity" in its calculation. Alkalinity is not pH, and is hard to understand.
http://www.baronchemicals.com/LSI RSI.aspx
LSI and RSI refer mainly to whether hardness materials are going to be deposited or removed, but the tendency to attack metals is related.

 

[Smooky]

The hardness level is low so that means there isn't much Calcium and minerals. That can cause the water to be corrosive.

 

[Reach4]

The hardness level is low so that means there isn't much Calcium and minerals. That can cause the water to be corrosive.

But then pH: 8.68 will work against attacking pipes. I have not run the calculator, but I expect he is fine.

 

[Gsmith22]

calculator said "serious corrosion" when I ran it. while influenced by pH, overall corrosion depends on overall water chemistry and sometimes lack of dissolved solids can be more detrimental than pH. Which is why demineralized water can be really corrosive even though its pH should theoretically be 7. Water wants to dissolve stuff regardless of pH.

 

[Smooky]

The hardness converts to 10.26 mg/l CaCO3 . Below 50 mg/l is considered corrosive.

 

[Reach4]

calculator said "serious corrosion" when I ran it. while influenced by pH, overall corrosion depends on overall water chemistry and sometimes lack of dissolved solids can be more detrimental than pH. Which is why demineralized water can be really corrosive even though its pH should theoretically be 7. Water wants to dissolve stuff regardless of pH.

What did you use as numbers? 10 is converted from 0.6 grains
121 was their suggestion for tap water if you don't know the number. Softeners don't affect carbonate much, AFAIK. I presumed "Hydrogen carbonate" was not the same as what the calculator wanted, but I could be wrong on that.

These numbers gave LSI=-0.12 from the cited calculator.

If I raise carbonate to 200, I get LSI=+0.10

I had lab tests on my raw water and treated ((H2S+iron) filter + softener) water.
Corrosivity, Langelier Index 0.7 raw 0.4 treated S.U
Corrosivity, Ryznar Index 6.4 raw 6.7 softened

I understand that my well water is very different from Detlev's.

 

[Gsmith22]

maybe I messed up. I used the 2.7 mg/l for the Ca as it is measured separately. 2.7mg/l for Ca and 0.6GPG for hardness don't seem to comport. isn't HCO3- hydrogen carbonate (measured at 0 mg/l)?

 

[Reach4]

maybe I messed up. I used the 2.7 mg/l for the Ca as it is measured separately. 2.7mg/l for Ca and 0.6GPG for hardness don't seem to comport. isn't HCO3- hydrogen carbonate (measured at 0 mg/l)?

Sometimes when they say calcium they mean calcium +magnesium's equivalent in calcium. That is what I assumed, since the calculator did not mention magnesium.

HCO3- hydrogen carbonate (measured at 0 mg/l) -- I don't know. Given that hardness is usually calcium carbonate and magnesium carbonate, I figured the carbonate would still be hanging around. So the zero number did not seem right to me. Again, that may have been a mistake.

 

[Gsmith22]

your confusion makes me feel better about my confusion Regardless of the correct numbers to be used in the Langelier index calculation, the larger point is still valid: water can be corrosive with a pH at or above 7. its the overall chemistry that matters more than just the pH

 

[DetRack]

But if I understand Langelier right, it's an old method that reduces corrosiveness on the effect that water has on calcium. If water reduces scale or dissolces calcium from mortat, it's consideed corrosive. If calciumcarbonate is precipitated, it's not corrosive.

Is that still a valid assumption? I read that while limestone protects from abrasion, it does not protect metal surfaces from rust and corrosion can even occur under a limestone layer.

 

[ditttohead]

Low levels of calcium do not make water corrosive. LSI, CI, Ryznar, all of these are algorithmic estimations, not conclusive in any way. Water has far too many variables to make any absolute statements about corrosivity. We use these equations as a good baseline so we know what is more likely to occur with the water. We will usually test for copper in the water in a copper plumbing system after a few months to see if we are causing any damage or if the water is corrosive. On the other end of the spectrum is "scaling" which can be just as bad as corrosive.

 

[Smooky]

Low levels of calcium do not make water corrosive. LSI, CI, Ryznar, all of these are algorithmic estimations, not conclusive in any way. Water has far too many variables to make any absolute statements about corrosivity. We use these equations as a good baseline so we know what is more likely to occur with the water. We will usually test for copper in the water in a copper plumbing system after a few months to see if we are causing any damage or if the water is corrosive. On the other end of the spectrum is "scaling" which can be just as bad as corrosive.

Calcium carbonate is often used to raise pH. I can’t believe you’ve never heard of that. So it is only reasonable that removing calcium will lower the pH.

CaCO3 calcium carbonate (calcite) has a pH of around 9.91, by adding it to the water such as in an acid neutralizer, will raise the pH and removing it in a process such as ion exchange will lower the pH.

There are many factors that affect the corrosivity of water such as pH, alkalinity, hardness, dissolved oxygen, total dissolved solids, temperature, flow rates, pipe materials and other factors. Determining whether the water is corrosive or not depends on many factors. Adjusting any one of these factors can influence corrosiveness.

 

[Reach4]

Calcium carbonate is often used to raise pH. I can’t believe you’ve never heard of that.

I think you misread something. I don't have a monopoly on that.

 

[DetRack]

Calcium carbonate is often used to raise pH. I can’t believe you’ve never heard of that. So it is only reasonable that removing calcium will lower the pH.

CaCO3 calcium carbonate (calcite) has a pH of around 9.91, by adding it to the water such as in an acid neutralizer, will raise the pH and removing it in a process such as ion exchange will lower the pH.

There are many factors that affect the corrosivity of water such as pH, alkalinity, hardness, dissolved oxygen, total dissolved solids, temperature, flow rates, pipe materials and other factors. Determining whether the water is corrosive or not depends on many factors. Adjusting any one of these factors can influence corrosiveness.

You are wrong. PH is a measure of ion content in the solution. When a softener removes CaCO3, the positive calcite ions are replaced by positive sodium ions. The number of positive ions in the water stays at the same level, and the pH is unchanged. If you read my laboratory results, you will notice that while I have very low Calcium content im the softened water, the PH value is still 8.6, which is basic, not acidic.

Yes, adding calcium to acidic waters neutralizes the PH. No, a water softener does not simply remove Ca+ from the water.

Osmosis water, rain water or distilled water are sour because they carry dissolved CO2. That is from completely different reactions and not related to a softener.

 

[Gsmith22]

there is a ton of misinformation in the last several posts that I think needs clarifying. pH is a measure of free H+ (hydrogen) ions in water relative to a neutral solution (pH of 7) where the number of H+ ions is equal to the number of -OH ions. A solution that is acidic has more H+ ions than neutral water. A solution that is basic has less H+ ions than neutral water. pH has nothing to do with CaCO3 and it isn't measuring the total ion content (which can include anything that will dissolve into solution).

A water softener is a specific cation ion exchange process where by positively charged ions are pulled from the water and (typically) replaced with Na+ ions. This can include anything that is positively charged but tends to favor Ca and Mg ions because they are both positively charged (+2 as well) and would rather not stay in solution (why they build up on pipes) relative to Na. The higher the positive charge (moving to the right on the periodic table) and the heavier the element (moving down the periodic table), the more a positively charged ion tends to get pulled out of solution and replaced with Na+ in the cation exchange process of a softener. This shouldn't cause any change in pH. I suggest reading this link for a better explanation of the process https://www.lenntech.com/Data-sheets/Ion-Exchange-for-Dummies-RH.pdf

I'll say it again, corrosivity is not solely dependent on pH. The various indexes mentioned attempt to capture (albeit imperfectly) this process. If you have copper pipes, a sure sign that water is corroding them are blue-green stains in sinks, tubs, and showers irrespective of pH measurements.

 

[ditttohead]

I did not want to go too technical in a DIY board, especially on a topic that really takes a good hour long training session to scratch the surface. Softeners have little affect on pH, as stated above. Ryznar, LSI and CI are all helpful but certainly not conclusive. They are nothing more than guidelines to point water treatment professionals in a certain direction. Testing for copper is a simple way to check corrosivity (if you have copper plumbing).

And why in the world would anyone think I have never heard of using calcium carbonate to raise pH? If you read through even a few of my old posts, I recommend that and other methods for raising pH consistently.