Well, if you apply enough voltage to anything, you’re guaranteed some kind of result, right?!

You might think water is well understood. But expose it to a few thousand volts, and you’ll find it still has a few tricks left.

Deionised water is a poor conductor — its resistivity is on the order of 18 MΩ·cm, meaning virtually no current flows under normal conditions. However, when the voltage is raised to kilovolt levels, the electric field strengths in the air gap reach ~10⁶  V/m, sufficient to ionise nearby gas molecules.

What you see above is a classic example: a faint violet arc bridging two 100 ml beakers. The colour comes from nitrogen plasma — the air itself breaking down under the intense electric field. As electrons accelerate across the gap, they collide with nitrogen molecules, knocking them into excited states. These promptly decay, emitting light at characteristic wavelengths (~390–430 nm).

What’s fascinating is that this isn’t really conducted through the water at all. It’s field ionisation of the air — a miniature corona discharge. And because deionised water can’t carry current internally, the setup behaves like a high-voltage capacitor, storing potential across the gap until discharge conditions are met.

But leave the system running with copper electrodes, and something else begins: electrolysis, ion migration, and the birth of less innocent species…

Note the beautiful- but quite harmful - chlorine compounds arising from prolonged electrolysis at the cathode. Chlorine hypochlorite is the most likely species, a common ingredient in bleaches. — Note the striking yellow-green tint forming around the copper cathode — an indication of chlorine-based species evolving during prolonged electrolysis. The most probable culprits are hypochlorite ions (ClO⁻), formed from chloride ions in the tap water under high voltage. These are key components in household bleach and are quite reactive — not something you’d want forming unchecked

Here’s the fascinating result of connecting the two beakers by high voltage: water threading

This isn’t ordinary conduction - it’s a dynamic structure formed (in theory!) by electrohydrodynamic forces pulling polar water molecules into alignment. Known as the floating water bridge in more advanced setups, this miniature version hints at the same underlying physics: polarisation, surface tension, and high electric field gradients acting together to defy gravity and cohesion limits.

If you want to go down a really interesting water-rabbit hole, look up “hydronium”. Sorry not sorry.

So what’s going on here?

This isn’t ordinary conduction, and it’s not electrolysis (yet). With ultra-pure water, the current is in the microamp range - far too low to generate visible bubbles or heat.

Instead, the electric field exerts a force on the polar water molecules, aligning dipoles and inducing a dielectric tension between the two liquid surfaces. Surface tension and capillary forces assist, but the bulk of the effect is due to Maxwell stress - the same principle that holds a dielectric in place inside a capacitor.

Eventually, impurities or ion migration begin to build up, and you may observe electrochemical reactions at the electrodes. Copper ions, hydroxide species, and even faint bubbling can appear if the current increases, degrading the effect over time.

Still, for a while, it holds - and that’s the fascination. Water shouldn’t hold itself up like a wire - gravity says it should fall. Yet under high voltage, polarisation and surface tension create a thread that defies intuition.

Final thoughts

The floating water thread isn’t just a lab-party trick; it’s a nice reminder of how matter responds to fields, outside of the normal ranges we see in everyday life. It blurs the line between physics and art, reminding us that even the simplest substance can surprise us under the right conditions.