Five-second answer

Claim we investigated

Pure water does not conduct electricity at all.

False. Water self-ionizes, so even ultrapure water conducts slightly; dissolved salts make tap water conduct far better. Pure water is often called an insulator, which is useful shorthand but not literally exact. Even without added salt, a small fraction of water molecules self-ionize, producing mobile hydrogen and hydroxide ions. Precision work reports a limiting conductivity near 0.055 microsiemens per centimeter and resistivity near 18.2 megohm-centimeters at 25 C. Those reciprocal values are temperature-specific. Ordinary water contains additional ions from dissolved minerals, salts, gases, and other substances, so it normally conducts far better. Ultrapure water also does not stay pristine when exposed to air or containers. This fact-check addresses material conductivity, not whether any electrical exposure is safe.

Quote or cite this fact-check

FactHub rates the claim “Pure water does not conduct electricity at all” False (high confidence): Water self-ionizes, so even ultrapure water conducts slightly; dissolved salts make tap water conduct far better. Reviewed October 6, 2026. https://facthub.org/n/article/pure-water-conducts-electricity-poorly/2

One-minute summary

What the evidence establishes

  • Pure water’s conductivity is very low but nonzero because water self-ionizes slightly.
  • At 25 C, the limiting values are about 0.055 µS/cm conductivity and 18.2 MΩ·cm resistivity.
  • Conductivity and resistivity are reciprocals, so the quoted pair describes the same 25 C benchmark.
  • Dissolved salts and minerals separate into mobile ions, making tap and natural water more conductive than ultrapure water.
  • Temperature, carbon dioxide from air, containers, and trace contamination can quickly change a high-purity sample’s measured conductivity.
  • Material conductivity alone does not determine whether an electrical situation is safe.
Important context: Fact check of the absolute claim that pure water has zero electrical conductivity. The article distinguishes intrinsic conductivity of pure H2O at 25 C from conductivity added by dissolved ions in real water samples and does not assess electrocution scenarios.

The evidence

The conclusion rests on the combined record. Expand each item to see its role and limitations.

Independence note: This check uses 3 methods across 4 institutions and 2 countries or international groupings.
Evidence map
Method Institution / country Year(s) What it shows Key limitation Primary links
Closed recirculating conductivity measurements and temperature-dependent coefficient analysis The Electrochemical Society publication record United States 2005 Light and colleagues measured and compiled fundamental conductivity and resistivity values for high-purity water from 0 to 100 C while analyzing temperature and impurity effects. At 25 C, the accepted limiting values are approximately 0.055 µS/cm conductivity and 18.2 MΩ·cm resistivity. The limiting benchmark describes highly pure water under controlled conditions. It is temperature-specific and difficult to maintain in an open vessel because trace ionic contamination changes the reading. T. S. Light, S. Licht, A. C. Bevilacqua, and K. R. Morash
International thermodynamic formulation and evaluated reference data International Association for the Properties of Water and Steam, National Institute of Standards and Technology International, United States 2024, 2025 IAPWS and NIST evaluate the ionization constant of water as a function of temperature and pressure. Near 25 C, pure water contains equal small concentrations of hydrogen and hydroxide species from self-ionization; their mobility makes conductivity nonzero even without added salt. The ionization constant alone does not equal conductivity: conductivity also depends on ionic mobilities and density. Both equilibrium and transport data are needed for the numerical conductivity value. International Association for the Properties of Water and Steam H. Arcis and A. Harvey, National Institute of Standards and Technology
U.S. Geological Survey educational synthesis of water-quality conductivity U.S. Geological Survey United States 2018 USGS explains that salts and minerals dissolved in water produce positively and negatively charged ions. These mobile ions raise electrical conductivity, which is why conductivity is routinely used as a water-quality measurement. The USGS page uses simplified language that calls pure water an insulator and says it does not conduct. The precision evidence shows that this should be read as very poor conductivity, not literal zero; the page also is not a safety standard. U.S. Geological Survey Water Science School
1. Precision measurements establish a small nonzero conductivity

Light and colleagues measured and compiled fundamental conductivity and resistivity values for high-purity water from 0 to 100 C while analyzing temperature and impurity effects. At 25 C, the accepted limiting values are approximately 0.055 µS/cm conductivity and 18.2 MΩ·cm resistivity.

Limit: The limiting benchmark describes highly pure water under controlled conditions. It is temperature-specific and difficult to maintain in an open vessel because trace ionic contamination changes the reading.

Verify: The Fundamental Conductivity and Resistivity of Water

2. Water’s ionization equilibrium supplies intrinsic charge carriers

IAPWS and NIST evaluate the ionization constant of water as a function of temperature and pressure. Near 25 C, pure water contains equal small concentrations of hydrogen and hydroxide species from self-ionization; their mobility makes conductivity nonzero even without added salt.

Limit: The ionization constant alone does not equal conductivity: conductivity also depends on ionic mobilities and density. Both equilibrium and transport data are needed for the numerical conductivity value.

Verify: Revised Release on the Ionization Constant of H2O Ionization Constant of Water

3. Dissolved ions explain why ordinary water conducts more

USGS explains that salts and minerals dissolved in water produce positively and negatively charged ions. These mobile ions raise electrical conductivity, which is why conductivity is routinely used as a water-quality measurement.

Limit: The USGS page uses simplified language that calls pure water an insulator and says it does not conduct. The precision evidence shows that this should be read as very poor conductivity, not literal zero; the page also is not a safety standard.

Verify: Conductivity (Electrical Conductance) and Water

Common questions

“If ultrapure water has any ions, it is not really pure.”

The hydrogen and hydroxide species arise reversibly from water molecules themselves. They are part of pure water’s equilibrium behavior, not necessarily foreign contamination.

“A conductivity value proves a water sample is chemically pure.”

Conductivity measures total ionic transport, not the identity of every substance. Different ion mixtures can yield similar readings, and nonionic contaminants may contribute little.

“Distilled water should always read exactly 0.055 µS/cm.”

That is a limiting 25 C benchmark. Distillation grade, temperature, dissolved carbon dioxide, storage vessels, handling, and trace residues can all produce a higher measurement.

“The low number means an electrical exposure involving pure water is safe.”

That conclusion does not follow. Conductivity is only one property in a hazard involving a source, current path, contact, time, body, environment, and protection. This article does not provide exposure guidance.

Conclusion

The accurate statement is that pure water conducts electricity very poorly, not that it cannot conduct. At 25 C, its limiting conductivity is approximately 0.055 µS/cm, corresponding to approximately 18.2 MΩ·cm resistivity. The small intrinsic conductivity arises from water’s ionization equilibrium and ion mobility. Ordinary water contains many more mobile ions and therefore generally has higher conductivity. Temperature and contamination matter, so figures reported without conditions should not be treated as universal constants. Confidence: High for the 25 C pure-water benchmark and the role of dissolved ions; actual samples vary with temperature, handling, and contamination.

How we checked

  1. Define pure water as the ideal high-purity limit, while separating it from ordinary distilled, deionized, tap, or natural-water samples.
  2. Anchor every numerical conductivity and resistivity statement to 25 C.
  3. Use the peer-reviewed transport study for the 0.055 µS/cm and 18.2 MΩ·cm benchmark.
  4. Use IAPWS and NIST evaluations for the temperature-dependent self-ionization equilibrium, without treating the equilibrium constant alone as a conductivity measurement.
  5. Use USGS only for the established role of dissolved ions in ordinary water and explicitly correct its zero-conductivity shorthand.
  6. Exclude electrocution thresholds, demonstrations, and procedural advice from the article’s scope.

Editorial note: Scope and safety: this article compares electrical conductivity of pure and ordinary water. It is not electrocution advice, does not identify safe voltages or conditions, and should not be used to plan contact between electricity, water, or people. Real injury risk depends on the source, current path, duration, body contact, environment, and protective systems in addition to the water sample. No external specialist review has been recorded. Readers can verify the numerical benchmark in the peer-reviewed conductivity paper and the temperature-dependent ionization basis in IAPWS/NIST materials.

Expert-review status

No external specialist review has been recorded. The primary measurement and authoritative thermodynamic sources are provided for direct reader verification.

Funding and conflicts

Funding: No external funding was received for this fact-check.

Ownership: FactHub is responsible for the article and its editorial process.

Conflicts: No known conflicts of interest are declared.

Sources

Sources are labeled by their role so readers can evaluate the evidence independently.

  1. Primary conductivity and resistivity measurement source T. S. Light, S. Licht, A. C. Bevilacqua, and K. R. Morash. The Fundamental Conductivity and Resistivity of Water DOI: 10.1149/1.1836121 Identifier: DOI 10.1149/1.1836121

    Peer-reviewed study reporting temperature-dependent fundamental conductivity and resistivity data for high-purity water and analyzing impurity effects.

  2. Authoritative ionization-equilibrium formulation International Association for the Properties of Water and Steam. Revised Release on the Ionization Constant of H2O Identifier: IAPWS R11-24

    International reference formulation for the ionization constant of ordinary and heavy water over temperature and pressure ranges.

  3. Evaluated reference record for water ionization H. Arcis and A. Harvey, National Institute of Standards and Technology. Ionization Constant of Water Identifier: NIST publication 958716

    NIST publication record for evaluated ionization-constant data in the CRC Handbook of Chemistry and Physics.

  4. Explanation of dissolved ions in ordinary water U.S. Geological Survey Water Science School. Conductivity (Electrical Conductance) and Water Identifier: USGS Water Science School conductivity article

    USGS overview of how dissolved salts and minerals provide mobile ions and why conductivity is measured in water-quality work.

  5. Article image source Wikimedia Commons. Conductivity meter Identifier: Wikimedia Commons file 18424462

    Source page for J C D’s photograph of an electrical conductivity meter, licensed CC BY-SA 3.0; FactHub’s crop and resize remain under the same license.

  6. study Fundamental conductivity and resistivity study

    Primary source for checking the high-purity-water benchmark and its temperature dependence.

    Identifier: light-water-conductivity-resource
  7. report IAPWS ionization constant release

    Authoritative formulation for checking the self-ionization equilibrium and its temperature dependence.

    Identifier: iapws-kw-resource

Update history

  1. Rating standardized under FactHub's verdict rules (was a free-text finding); the headline now states the finding. The evidence and conclusion are unchanged.
  2. Initial final article clarifying that pure water has low but nonzero conductivity, with all numerical benchmarks anchored to 25 C and safety advice excluded.

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