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Answer: Conductivity is a measure of the ability of water to pass an electrical current. Pure water is actually an excellent insulator and does not conduct electricity, but water stops being an excellent insulator once it starts dissolving substances around it.

Why natural water conducts

Water can dissolve more things than just about any other liquid. The most common dissolved substances are salts, which are ionic compounds composed of cations (positively charged ions) and anions (negatively charged ions). Even a small amount of ions in a water solution makes it able to conduct electricity.

What changes conductivity

• Because dissolved salts and other inorganic chemicals conduct electrical current, conductivity increases as salinity increases.
• Organic compounds like oil do not conduct electrical current very well and therefore have a low conductivity when in water.
• Conductivity is also affected by temperature: the warmer the water, the higher the conductivity.

How it is measured

USGS scientists almost always measure the conductivity of water when water samples are collected. The conductivity is measured with a probe called a conductivity cell.

Why it is useful

Conductivity is useful as a general measure of water quality. Each water body tends to have a relatively constant range of conductivity that, once established, can be used as a baseline for comparison with regular measurements. Significant changes in conductivity could then be an indicator that a discharge or some other source of pollution has entered the aquatic resource. Generally, human disturbance tends to increase the amount of dissolved solids entering waters, which results in increased conductivity.

Claims

• id: C1 claim: Pure water is an excellent insulator. source: S1 evidence: "pure water is an excellent insulator and does not conduct electricity."
• id: C2 claim: Conductivity is measured with a probe called a conductivity cell. source: S1 evidence: "The conductivity is measured with a probe called a “conductivity cell”"
• id: C3 claim: Conductivity increases as salinity increases. source: S2 evidence: "conductivity increases as salinity increases."

Sources

• [S1] Conductivity (Electrical Conductance) and Water. USGS. https://www.usgs.gov/special-topics/water-science-school/science/conductivity-electrical-conductance-and-water . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Indicators: Conductivity. EPA. https://www.epa.gov/national-aquatic-resource-surveys/indicators-conductivity . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

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  author = {{iinventedlight}},
  title = {{Electrical conductivity of water}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/electrical-conductivity-water/},
  note = {Permanent ID iil:note:bk89s0dc. License: CC-BY-4.0.},
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