The authoritative public forum
  for Metal Finishing since 1989
-----

What is the definition of "Water Conductivity"

I'm actually working on a project involving water boiling towers; we had a little problems concerning water conductivity: the declared "acid water conductivity" is (I seem to remember) 0,25 mSv, while the "total water conductivity" is 0,10 mSv (the second lesser than the first).

Now, if the acid conductivity is the cation conductivity, I can't understand how can be possible the cation+anion conductivity be lesser than the lonely cation one.

I'd like to know how is DEFINED the conductivity and the acid conductivity, to understand if there is some reason for such a situation or if I have to call and start asking what they told wrong.

Alberto Vezzoli
- Milano, Italy
2005

---

I have just reviewed a McGraw-Hill Dictionary of Scientific Terms and Abbreviations and can not find your terms or abbreviations. Conductivity is usually considered the reciprocal of resistance and is expressed in Siemens (S) (formerly called mhos). There is only one conductivity of a given solution that I can find, just as you would measure one resistance. Those little electrons don't care what carries them or what stands in the way. They either make it or not. Can you please define the unit of measure, so I can learn.

Paul Morkovsky
- Shiner, Texas, USA
2005

Setting aside the unit confusion, conductivity is a function of the ability of the solution to transport charge. At the anode, water is oxidized, or a reactive ion gives up an electron, while at the cathode, water is reduced, or a reactive ion takes on an electron. Therefore, acid water conductivity may be higher due to the presence of protons.

Juzer Jangbarwala
- Brea, California
2005

---

It is all a matter of "specific wording" dedicated to the way the Power Industry spells the water quality specification: basically the TDS make sense through the water conductivity, but this is not sufficient to describe the potential risk for corrosion at the boiler stage, and in order to have a meaningful description of the risk assessment, most boiler manufacturers specifies, max. TDS and cationic conductivity which is not the conductivity of the cation BUT the one produced after passing the water through a strong acid cation resin in H+ form which will indicate the level of strong anionic species such as Cl- and SO4-- that will be highly detrimental to high pressure boiler.
One should say acid conductivity and not cationic conductivity.
From this definition, it is quite easy to understand why a water could be < 0.1 µS/cm and at the same time have <0.25 µS/cm as acid conductivity, knowing that strong acids have 3 to 5 times higher conductivity when compared to their sodium salt.Please refer to conductivity table.

Andre Medete
- Marienthal, France
February 6, 2010