The oxidation number of hydrogen in water is +1. In the neutral molecule H₂O, each hydrogen is assigned an oxidation number of +1 and oxygen is assigned −2; the total is therefore zero, matching the molecule’s overall electrical neutrality.
An oxidation number is a bookkeeping value used to track how electrons are distributed in compounds. It does not necessarily mean that a hydrogen atom literally carries a full positive charge. In a water molecule, oxygen attracts the shared bonding electrons more strongly than hydrogen does, giving oxygen a partial negative charge and the hydrogen atoms partial positive charges.
The +1 rule applies to hydrogen in most compounds, including acids, alcohols, and water. The important exception is a metal hydride, such as sodium hydride (NaH), where hydrogen is assigned −1 because sodium is more electronegative by the conventions used for oxidation states. Another common mistake is to confuse oxidation number with ionic charge: water contains covalent bonds and is not made of H⁺ and O²⁻ ions under ordinary conditions.