The water droplet test tells you, without a thermometer, whether an uncoated frying pan is hot enough to cook with. If a drop of water sizzles away, keep heating; if it pulls into a single bead that glides across the surface, the pan is ready for oil or butter. That gliding bead is the Leidenfrost effect.
Key points
- Preheat the empty, dry pan over a medium heat, then flick in a few drops of water.
- If the drop sizzles away, the pan is not hot enough yet.
- If one bead holds together and glides, turn the heat down slightly, add fat, then the food.
- Never do this with a non-stick (PTFE) pan, which should not be heated empty.
This guide explains the science, the three stages to look for and the mistakes that throw the test off. If food still sticks after proper preheating, see our guide on why food sticks to a pan for the other causes.
What is the Leidenfrost effect?
When water lands on metal far hotter than its boiling point, the underside of the drop turns to steam instantly. That steam forms a thin cushion that lifts the rest of the drop off the metal. Because steam is a poor conductor of heat, the drop evaporates much more slowly and skates around instead of boiling away. Physicist Jearl Walker of Cleveland State University puts the thickness of this vapour layer at only about 0.1 to 0.2 mm.
The effect is named after Johann Gottlob Leidenfrost, a German doctor who described it in 1756.
What is the water on pan trick?
It is simply using that effect as a heat gauge. Which? recommends it for stainless steel: heat the empty pan for a minute or two, add a drop of water, and if it beads up and glides around, the pan is ready. Here is what you will see along the way.
| What you see | What it means | What to do |
|---|---|---|
| The drop spreads out, sizzles and disappears within seconds | Hot, but below the Leidenfrost point: the water is touching the metal and boiling | Keep preheating |
| The drop breaks into small beads that skitter and hiss away | Transition: the vapour layer keeps forming and collapsing | Wait a little and test again |
| One bead holds together and rolls around like mercury | The vapour layer is stable: the pan is hot enough | Turn the heat down slightly, add fat, start cooking |
Walker measured how long drops survived on a heated plate. Between 100 and about 200 °C they spread out and vaporised quickly; at about 200 °C they beaded up and lasted more than a minute.
Why it helps stop food sticking
Your food does not float on a cushion of steam the way the drop does. The test is a thermometer substitute: it confirms the pan is properly preheated before the fat and food go in. In a pan that is too cold, meat releases its juices, stews and sticks. In a well-preheated pan with a little fat, a crust forms. As Which? puts it, food like steak or chicken skin will naturally release when it is ready to be flipped.
One scientific caveat. The Leidenfrost temperature is not a fixed number. Wakata and colleagues (2023) measured it on several metals and found it rises with surface roughness and is higher on stainless steel than on aluminium, because stainless steel is slow to replace the heat the drop draws from the spot beneath it. A surface does not create the effect; a rougher one actually needs more heat to reach it.
How to do the water droplet test
Stainless steel frying pan
- Put the clean, dry pan on a medium heat and let it warm up empty for a minute or two (Which?).
- Flick in a few drops of water with your fingertips.
- Wait for one bead that holds together and glides. Wipe out any leftover water with kitchen paper.
- Turn the heat down a notch, add oil or butter, then the food.
- If food sticks, do not force it: let it release on its own.
Cast iron or carbon steel
- Preheat slowly. Lodge recommends 3 to 5 minutes on a medium-low heat to avoid thermal shock.
- Do the test: Lodge says water that dances when it hits the pan means you are at the right temperature.
- On an induction hob, Lodge suggests preheating slowly with oil instead. You cannot use the water test then; the pan is ready when the oil shimmers and ripples.
Uncoated titanium cooking surface
- Treat it like stainless steel. Titanium conducts heat about as slowly, so preheat patiently over a medium heat.
- Test in two places, the centre and near the edge, as heat spreads more slowly than in aluminium.
- On a hammered surface, the bead may sit in one of the dimples. Walker actually hammered a dent into his test plate to hold drops in place. So look at whether the drop stays whole, not at how far it rolls.
- Turn the heat down slightly, add fat, then the food.
This is how to use the Untitan pan: titanium cooking surface, uncoated, PFAS-free, which works on every hob, induction included, thanks to its stainless steel base. The hammered surface, well preheated with a little fat, makes food easier to release; without preheating and fat, it sticks like any uncoated pan. We cover titanium's other limitations honestly in titanium cookware pros and cons, and eggs get their own guide: how to stop eggs sticking to the pan.
Common mistakes
- Too hot: a drop will still glide on an overheated pan, so the test has no upper warning. The oil tells you: if it smokes, the pan is too hot. Lodge advises taking it off the heat for a minute or two before cooking.
- Too cold: adding fat at the first sizzle means cooking in stage one. Give the pan time.
- Wet from the dishwasher: leftover water has to boil off first and mixes with your test drops. Dry the pan before heating it.
- Induction on full power: induction heats the pan directly and fast. Which? found the best induction hobs bring pasta water to a rolling boil in about half the time of the best gas hobs. Preheat on a medium setting and skip the boost function.
- Water into hot fat: always test before adding oil, or it will spit.
Never use this test on a non-stick pan
The test means heating a pan empty, which is exactly what you should not do with a PTFE-coated (Teflon-type) pan. Germany's Federal Institute for Risk Assessment (BfR) says PTFE can start to break down from about 360 °C, releasing substances hazardous to health without visible smoke, so coated cookware should never be heated when empty. It adds that particular care is needed with induction and gas, which heat very quickly.
Frequently asked questions
How do you achieve the Leidenfrost effect?
Preheat a dry, uncoated pan over a medium heat until a drop of water forms a single bead that glides instead of sizzling away. On metal, that happens at around 200 °C, depending on the material and surface.
What happens when Leidenfrost is too hot?
The drop keeps gliding, so the test will not warn you. Watch the oil instead: smoke means the pan is too hot, so take it off the heat briefly.
Can you do the water droplet test on a non-stick pan?
No. The BfR advises never heating PTFE-coated pans empty.
Sources
- Jearl Walker, Cleveland State University: Boiling and the Leidenfrost Effect
- Wakata et al., How roughness and thermal properties of a solid substrate determine the Leidenfrost temperature (2023)
- Wikipedia: Leidenfrost effect
- Which?: How to buy the best stainless steel pans
- Which?: 5 things you should know before switching to an induction hob
- Lodge Cast Iron: How to Use Cast Iron Over Any Heat Source
- Lodge Cast Iron: Can I Use Cast Iron on an Induction Cooktop?
- BfR: Selected questions and answers on cookware, ovenware and frying pans with a non-stick coating made of PTFE
- Engineering ToolBox: thermal conductivity of metals