Conductivity:
Conductivity will extremely quickly denote the presence of any ionic impurities, even if the impurity concentration is very small. As an instance, suppose 1.0 mg of NaCl impurity were deposited in 1 liter of demineralized water. The routine of this solution would be as follow.
1 × 10-3 (gm/ liter) × (1 equivalent/ 58 gm) = 1/58 × 10-3 (equivalent/liter) = 1.7 × 10-5 (equivalent/ liter)
The equivalent conductance of Na+ is 51(mhos- cm2/ equivalent), therefore the equivalent conductance of Cl- is 75(mhos cm2/ equivalent). The conductivity of the solution is (51 + 75) (mhos- cm2/ equivalent) × 1.7 × 10-5 (equivalent/ liter) × 10-3 (liter/ cm) × 106 (µmho/ mho) = 2.2 (µmho/ cm).
that is well above the limit. Even very low concentrations of ionic impurities could simply be detected. The most probable cause is a damaged or depleted resin bed that is no longer capable of erasing ionic contaminants. The depleted bed should be erased from service, or a fresh resin bed placed in service.
For most applications within nuclear facilities, the specification which is recognized as Very Pure (1.0 µmho/cm maximum conductivity) is used. The Ultra Pure demineralized water is generally only needed in laboratory situations and is mentioned for information purposes only.