VPE 511: Environment and Environmental Hygiene (2+1)

ELECTRICAL CONDUCTIVITY

• Chemically pure water is a non-conductor of electricity, but the solution in it of ionisable salts renders it conducting, the case with which an electric current is transmitted being directly proportional to the concentration of ionisable salts in solution. This fact is made use of in the examination of natural waters, the electrical conductivity of the water being an indirect measure of the amount of dissolved substance present it.
• It should be noted that, by itself , the electrical conductivity gives no indication of the nature of the substances in solution.
• Values of electrical conductivity for natural waters vary from about 100 gemmhos for soft waters derived from the older crystalline rocks to about 2,000 gemmhos for very hard waters derived from the newer and softer rocks; sea water has a conductivity of about 50,000 gemmhos.
• In the absence of sodium salts, the electrical conductivity is proportional to the hardness, one degree of hardness raising the electrical conductivity by about 20 units. Thus such a water with a conductivity of 500 units , would possess a hardness of approximately 25⁰.
• The determination of electrical conductivity finds its greatest use in indicating changes in the amount of dissolved solids present in a water where the composition of the dissolved solids fraction is known and is fairly constant.