1 × 103gm
1.7 × 105equivalent
Principles of Water Treatment
Conductivity is a measure of the ease with which electricity can be passed through a substance.
The presence of ions greatly facilitates the passage of an electric current. Pure water is only
slightly ionized by the dissociation of water: H O H + OH . At 25 C, the concentration
of the hydrogen and hydroxyl ions is 10 moles/liter.
The equivalent conductance of hydrogen (H) is
and the equivalent conductance of OH is
A mho is a measure of the ease with which electric current will pass and is the inverse of an
ohm, the measure of resistance to the passage of electric current. Conductance and
conductivity are similar qualities (conductivity is measured in
, so conductance must
be converted to conductivity). A mho is one millionth of a mho. The total conductivity of
pure water can be calculated by adding the equivalent conductances of H and OH, multiplying
by the normality (see Module 1 for definition), and then multiplying by
. For theoretically pure water this becomes the following.
The conductivity limit for demineralized water is 1
Conductivity will very quickly indicate the presence of any ionic impurities, even if the impurity
concentration is extremely small. As an example, suppose 1.0 mg of NaCl impurity were
deposited in 1 liter of demineralized water. The normality of this solution would be as follows.