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This question already has an answer here:

From my understanding water shouldn't really damage electronics, but it does. what about water actually causes damage, and why is water with impurities such as salt make it so much worse?

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marked as duplicate by Null, JRE, PeterJ, Ricardo, Daniel Grillo Sep 24 '15 at 14:24

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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There is nothing inherent about water that will damage electronics. There have even been experiments where electronics have been operating while immersed in pure water.

The impurities on the other hand can both conduct electricity and corrode the materials the electronics are made from. The former will cause unintended shorts, and the latter will destroy the electronics directly.

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  • \$\begingroup\$ While I basically agree with your answer, it is worth noting that very pure water is highly corrosive in itself because it is such a good solvent. So, if one operates a circuit under deionized water, while it will probably work initially (unless the circuit is very sensitive to parasitics), it will probably not remain operable indefinitely unless protected somehow. \$\endgroup\$ – Oleksandr R. Sep 24 '15 at 11:18
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You state 'From my understanding water shouldn't really damage electronics'. I think that's just plain wrong, for several reasons. Several things.

  1. Water is a conductor, though a poor one (see here). At 182kΩm (or 5.5 micro-siemens/m see here and convert to SI units), across a short distance (e.g. 1mm) and with long tracks that could lead to a non-negligible conductance, which is enough to affect a circuit's operation. This won't itself permanently damage the electronics (i.e. the circuit drying will fix it) but if the circuit is operated when wet, excess current may flow causing permanent damage, especially with high voltages present.

  2. Whilst water is a poor conductor, gunk on the board may dissolve in water, decreasing its resistance further, possibly quite dramatically, increasing the effects in (1). Impurities already in the water may do the same thing.

  3. When current flows through water, positive ions will flow in the direction of the current flow. This will cause PCB tracks etc. to be gradually electrolytically dissolved. This may cause permanent damage if operated when wet.

  4. Various materials within the electronics may dissolve in or be damaged by the water, for instance paper within paper capacitors, cardboard speaker cones, etc. This may cause permanent damage if wet (whether or not operated).

  5. Water leaking into air-based capacitors is likely to change their capacitance, and the additional parasitic capacitance of water surrounding the tracks is likely to change circuit performance. This will only affect the operation of the circuit when wet, and is unlikely to cause permanent damage unless it causes excess current to flow.

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    \$\begingroup\$ Be aware that the m in kΩm is actually m^2/m. So you have 182Ω for conductors of 1m^2 surface area separated by 1mm thickness of water, which is not a very realistic scenario. If the area of the conductors is 1cm^2 then the resistance will be 1.82MΩ, which is still potentially significant but perhaps not such a severe problem. \$\endgroup\$ – Oleksandr R. Sep 24 '15 at 11:25
  • \$\begingroup\$ @OleksandrR. - doh, yes. I thought it seemed a bit low. Edited. \$\endgroup\$ – abligh Sep 24 '15 at 11:29
  • \$\begingroup\$ (No other answer here states 182kΩm, or indeed 182 anything. It is mentioned in a comment by Ignacio Vazquez-Abrams, though. Was that what you meant?) \$\endgroup\$ – a CVn Sep 24 '15 at 13:08
  • \$\begingroup\$ @MichaelKjörling thanks, yes that's what I meant, though I have now independently sourced it (which I was too lazy to do to start off with) and edited the answer appropriately. \$\endgroup\$ – abligh Sep 24 '15 at 13:37
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Water has a dielectcic constant of about 80 when pure .This would raise parasitic capacitances everywhere which would muck up resonant circuits ,slow down high speed digital waveforms causing malfunction.It could make some equipment go unstable.

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A small amount (1 in 10^7) of water molecules (in pure water) break into H+ and OH-. These can conduct electricity and hence mess up your circuit.

https://en.wikipedia.org/wiki/Self-ionization_of_water

Impurities, specifically ions (charged particles) improve conduction (significantly) and hence increase the damage.

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    \$\begingroup\$ At 182kΩm it isn't a particular good conductor, so the circuit would have to be very sensitive for it to have an effect. \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 24 '15 at 8:15

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