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What experiments showed that water is made of hydrogen and oxygen?

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water rapids, Niagara Falls, Canada — water Water is the most plentiful compound on Earth and is essential to life. Although water molecules are simple in structure (H₂O), the physical and chemical properties of water are extraordinarily complicated.

The composition of water as a compound of hydrogen and oxygen was established through two primary experimental approaches in the late 18th and early 19th centuries:

Synthesis by Combustion: In 1781, Henry Cavendish demonstrated that water is produced by burning "inflammable air" (now known as hydrogen) in "dephlogisticated air" (now known as oxygen). Antoine-Laurent Lavoisier later confirmed this, identifying water as a chemical compound of these two substances and renaming them accordingly.123
Decomposition by Electrolysis: Shortly after the invention of the battery in 1800, William Nicholson and Anthony Carlisle used an electric current to perform electrolysis on water. By passing current through water, they successfully liberated hydrogen and oxygen gases, proving that water could be broken down into these constituent elements.4

These experiments were foundational to the chemical revolution, moving science away from the phlogiston theory and toward a modern understanding of chemical composition.13