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Water Quality Assessment: Chemical: Conductivity and Density
Conductivity is the ability of water to carry an electrical current. It indicates the physical presence of dissolved chemicals in the water. For example, when sodium chloride (NaCl, table salt) dissolves in water, it dissociates into Na+ and Cl- ions. The movement of these ions conducts electricity through the water. The dissociation of naturally-occurring, inorganic compounds is the main source of ions in stream water. Conductivity can also increase as a result of heavy metal ions released from pollutants such as acid mine drainage.

To "see" the electrical current being carried by Na+ and Cl- ions, try the following activity. First, connect the positive terminal of a battery to an electrode. Place the electrode in a glass of deionized water. Next, connect the negative terminal of the battery to a light bulb, then connect the light bulb to an electrode. Place the electrode in a glass of deionized water (see animation below). Notice that the light bulb does not glow. Add some salt (NaCl) to the deionized water (see animation below). Notice that the light bulb starts to glow. That is because the Na+ and Cl- ions complete the circuit between the positive and negative electrodes. They enable the electrical current to flow through the circuit.

Image showing the difference of a battery connected to deionized water without salt and deionized water with salt. Please have someone assist you with this.

Like conductivity, water density is an indicator of the physical presence of chemicals in water. The density of water is related to salt content and water temperature. This is a very useful parameter to measure because the salinity of a body of water is one of the main factors determining what organisms will be found there.

 

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