This is a bit of a trick question! Both distilled and tap water are primarily made of H2O, meaning they have the same basic composition of hydrogen and oxygen.

Here's why it's tricky:

* Distilled water has had almost all impurities removed, including minerals. This might make you think it has *less* hydrogen, since minerals often contain other elements. However, the hydrogen content of the water itself is not affected by this process.

* Tap water contains dissolved minerals, which are not pure hydrogen.

So, the bottom line is: both distilled and tap water have the same percentage of hydrogen by mass (around 11.19%). The difference is in the presence of other elements, but not in the *amount* of hydrogen present.