Explanation

The ratio of hydrogen to oxygen by mass in water is always 1:8. 

This ratio is derived from the atomic masses of hydrogen (approximately 1 g/mol) and oxygen (approximately 16 g/mol) in the water molecule (H₂O),

Where there are two hydrogen atoms and one oxygen atom.

Therefore, the mass ratio is (2 * 1) : 16, which simplifies to 2:16 or 1:8.