1. Saltwater: This includes all the oceans, making up the vast majority of Earth's water.

2. Glaciers/Ice Caps: These hold a massive amount of frozen water, especially in places like Greenland and Antarctica.

3. Groundwater: This is water found beneath the surface, in aquifers. It's a significant source of drinking water.

4. Rivers/Lakes: While these are important for ecosystems and human use, the total amount of water they hold is relatively small compared to the others.