You're close! While water is incredibly abundant on Earth, it's not the most common substance. The most common substance on Earth is actually iron.

Here's why:

* Earth's core: The Earth's core is primarily composed of iron, making up a significant portion of the planet's mass.

* Water's distribution: While water covers a large portion of the Earth's surface, it's distributed across oceans, rivers, lakes, and groundwater. The Earth's overall mass is far greater than the mass of all the water combined.

So, even though water is essential for life and covers a large portion of the Earth's surface, iron wins out in terms of overall mass and abundance.