The data supports that water has a definite and constant composition. For every 11.1 parts by weight of hydrogen, there are 88.9 parts by weight of oxygen in a sample of pure water. This is a fundamental characteristic of water, regardless of its source, whether it comes from a tap, a river, a lake, or the ocean. This constant composition reflects the fixed ratio of hydrogen and oxygen atoms in water molecules (H2O), reinforcing the notion that water is a compound with a specific chemical formula. Scientists refer to this idea as the law of definite composition or constant composition.