The balanced equation for the reaction of sulfur dioxide (SO₂) with water (H₂O) is:

SO₂(g) + H₂O(l) ⇌ H₂SO₃(aq)

This reaction produces sulfurous acid (H₂SO₃), which is a weak acid. The reaction is reversible, meaning that sulfurous acid can also decompose back into sulfur dioxide and water.