Water is a dielectric and thus an insulator allowing electric current only to flow when ionic material is present. The more ionic matter in
the water the higher the conductivity and the less ionic matter the lower the conductivity will be. Both electrolysis and electrochemistry
are involved. Electrolysis is water containing ionic matter and in particular salts and electrochemistry is a useful tool in the purification
of metals, production of nanometre sized atomic silver clusters, wet photo chemistry and metal plating. Both forms are considered wet
chemistry, albeit, mostly in the realm of physics. Somewhere along the way, chemists introduced the concept of ‘wet’ conductivity
measurement for conducting water and also introduced fraction of the Siemen to depict variations of the Siemen such as milli and microSiemen.
Soon however, the DC measurement technique in vogue as MHO, (the reversal of OHM) was abandoned and a version having
alternating current as its basis was introduced and adopted. Ever since that day, there have been numerous problems.
A recent encounter with a questionable claim of very pure water
has prompted me to analyse exactly what we are all facing when
relying exclusively on conductance measurements expressed in
milli and micro Siemens. The particular water quoted as being a
“steamed distilled water’ measured initially 1 uS/cm and shortly
thereafter 2 uS/cm. However when the actual resistivity was
measured it only came to 100,000 Ohm/cm when it should have
been the reciprocal value of 1 million Ohm for the first reading.
Having exclusively used deionised water for my electrochemical
experiments, I was surprised that the normal 500uA/h had reduced
to a mere trickle of just 9uA/h using the steamed distilled water.
Many months earlier the same thing had happened. Thinking my
equipment was somehow at fault and having insufficient current
capacity, I undertook a complete rebuild. Unfortunately it was all a
waste of time. It was the water somehow or what was in there that
opposed the flow of current. At that point I decided to investigate
what caused the reduced current flow.
My first pont of call was the supplier of the water, but that also
proved to be a waste of time. However somewhere along the time
I acquired two test reports that are starting to explain what may
be the cause of the current impediment. Before I am able to go
further, let us look at some facts.
Facts and fallacies.
1. The Term Siemens came first on the scene in the late 1800s,
when a German engineer and inventor named Werner von Siemens
created an Ohmic standard for a length of copper telegraph cable.
This took the shape of a column of Mercury that measured 0.95
Ohm, a very low DC resistance for a solid.
2. The term Mho was introduced soon after in order to establish
the reciprocal of Ohm in measuring a DC electric current flow over
a specific distance, i.e. a metre, decimetre or centimetre.
3. Dissatisfied with the concept of MHO, that term was replaced
by Conductance over 1 cm (10mm) for measuring the electrical
current flow in water and its reciprocal of Resistivity/cm in line
with Ohms law.
4. Due to the perceived polarisation of water DC, MHO
measurements were replaced by Alternating Current irrespective of
its frequency dependence. This reciprocal range is supposed to be something like the chart hereunder, starting from a low resistivity
(1 Ohm) and very high conductance to a very high Resistivity (100
M Ohm) and a very low Conductance.
1 Ohm/cm = 1 Siemens/cm
10 Ohm/cm = 100 milli S/cm
100 Ohm/cm = 10 mS/cm
1 K Ohm/cm = 1 milli S/cm
10 k Ohm = 100 uS/cm
100K Ohm = 10 uS/cm
1 M ohm = 1 uS/cm
10 M Ohm = 0.1 uS/cm
100 M Ohm = 0.01 uS/cm
Sometimes a questionable anomaly is included that claims a
resistivity of 18.24 M Ohm (conductivity of 0.0548 uS/cm) at a
pH of 7, where water is claimed to be neutral, (neither acidic and
below 7) or (alkaline and above 7). And here it is where everything
There appears to be no verification that all of the values of
Conductance are in fact the reciprocal of the corresponding
resistivity values. Well, how could anyone. Conductance is a
measured current at Alternating Current and resistivity can only be
measured by DC, but let me explain.
5. So-called AC resistance is actually properly referred to as an
Impedance. It is also frequency dependent. An impedance at 100
Hz is different to an Impedance at 1,000Hz and an impedance at
radio frequencies is different again. DC resistance however has
nothing whatsoever to do with frequencies and is just DC or Direct
Current as from a battery.
It does not have an impedance but instead
refers to a high or low resistance input or output. AC impedances
are what it says. There is an impediment or opposition to the flow
of electrical current caused by the introduction of electro-magnetic
field force lines.
6. Polarisation of the electrical properties of unpure water, other
than the dipolar charge of the water molecules, i.e. positive for
Hydrogen and negative for Oxygen. With the equilibrium voltage
of water being 1.23 volt DC, introducing such and higher voltages
in the water is going to interfere with its stability.
7. Water has dielectric properties and is thus an insulator, measuring
very high resistance values the purer (or less contaminated) it gets
resulting in allowing only minute currents to flow, Tera ohms in
resistance and Pico ampere in current. To measure such values
is beyond conventional test equipment and in particular a hybrid
Conductance/Resistivity instrument like a conductance meter
operating on AC. To also expect such Conductance meters to also
measure non-conduction materials such as neutral metals, organics
and pathogens is wishful thinking.
8. There is always the problem in describing the concept of
dissolved solids. Some scientists just relate this to ionic matter,
but the truth is that total dissolved solids can mean matter in the
water DISSOLVED OR NOT can have an adverse effect on the
purity or quality of the water. Processes of the water to remove
ionic matter and metallic salts may still contain harmful materials
such as pharmaceuticals as well as recombinations of these drugs,
hormones and pathogens.
For that type of contamination, knowing
the Conductance factor in micro Siemens is useless. Perhaps we may
have to revisit the old analogue test equipment used in the 1900s
such as the Turbidity, Nepholometer and other such equipment for
physical observation of some of these dissolved organic matter.
I am just completing such an instrument for personal use. It uses
cross polarised light scattering principles that under violet light
can make very small particles visible and quantifiable.
There is a need for something better. Perhaps in the area of analogue
electronics where indeed measuring instrumentation can go much
lower and higher parameters of pure and unpure water by factors
of millions in some areas. When testing water we simply cannot
rely on just a conductance measurement and hope we measured it
all. That is simply not true.