Factors affecting the conductivity of water
Electrical conductivity is the property of water to conduct electricity from an area of high electric field to an area of low electric field, with the help of dissolved ions that act as conductors. An ion is an atom that is freed from an element and carries either a positive charge or a negative charge. Although metals are far more effective conductors, water also has the ability to conduct electricity. There are several factors that affect the electrical conductivity of water, such as TDS (Total Dissolved Solids, or concentration of salts in water), mineral purity and temperature of water.
Factors that affect the conductivity of water
Total Dissolved Solids (TDS) / Salinity
Salt water conducts electricity much effectively and more readily than pure water. Since dissolved ions enhance salinity as well as increase conductivity, it is routinely used to calculate electrical conductivity. Salts ions that usually cause salinity are sulphates, carbonates, chlorides, potassium, sodium, calcium and magnesium. Electrical conductivity will change with the kind of water source – groundwater, runoff water, water drained from agricultural fields and rainfall. Therefore, sub-factors such as geology, soil, land use and flow of water (conductivity increases as water flow decreases) also affect the salinity of water, thus influencing electrical conductivity.
The electrical conductivity of pure water is low, but it can be greatly increased by soluble impurities that will ionize in water (such as common salt). Pure water consists of one oxygen and two hydrogen atoms. The oxygen atoms share covalent bonding (with their outermost electron shells) with the two hydrogen atoms, completing their octet of outermost shell. Therefore, one oxygen atom can bond covalently with two dihydrogen molecules (two bonded hydrogen molecules). Electricity travels easily and readily through materials having atoms that form an ionic bond. Oxygen atoms in the water molecule pull the electrons strongly, thereby developing a negative charge. The dihydrogen forms a positive charge, thus resulting into negligible transfer of electric flow. If minerals as impurities are added in water, the ionic bonds conduct electricity and the electrolytic conductivity of water increases.
Electrical conductivity in water invariably increases with an increase in temperature, as opposed to metals. Warm water is less viscous and has greater electronic movement, thus allowing free flow of electric current. It is generally expressed as a relative change per degree Celsius, at a particular temperature. Small variation or difference in temperature reports a marked difference in conductivity and therefore, readings are normally referenced to 25C. Generally, conductivity increases by about 2% for every degree rise in temperature (range being 1 to 3 %).