350^mhos   cm 2 equivalent 192^mhos   cm 2 equivalent. µmhos/cm 10³  l/cm³ 10⁶  µmhos/mho (350 ₁₉₂₎mhos cm² equiv ×  10^7equiv liter ×  10^3liters cm³ ×  10^6µmhos mho .054^µmho cm µmho/cm _{1   ×  10³}gm liter ×^{1  equivalent} 58  gm 1 58 ×  10^3equivalent liter 1.7  ×  10^5equivalent liter Principles of Water Treatment DOE-HDBK-1015/2-93 WATER PURITY Rev. 0 CH-04 Page 29 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 2 + - of the hydrogen and hydroxyl ions is 10   moles/liter. -7 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 and .  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.