In this video, we'll follow the journey of water from its descent as rain to its role as groundwater and how humans have managed and used it throughout time. When rain falls, it infiltrates the ground. On sandy shores, it happens quickly because sand absorbs water easily. The water that soaks into the ground becomes soil water, filling the spaces between the grains. As the water continues its journey downward, it accumulates beneath the surface, creating a reservoir of water between the sand grains. This is known as groundwater and as we've already covered in previous chapters, groundwater plays a vital role in supporting ecosystems as well as human life. And for this reason, humans have long developed ways to manage water resources and control the flow of freshwater to ensure a supply for drinking, livestock, and daily activities such as washing.

The ancient city of Jerash is a remarkable example of advanced Greco-Roman water management. It's estimated that up to 95% of this average Roman city in the Levant had access to running water. This was made possible by a network of impressive aqueducts, underground channels and cisterns that supplied water for public baths and even fountains. Another example of climate-smart water management is the ancient city of Great Zimbabwe. For over 1,000 years, its people effectively managed various water sources, including groundwater wells and even enhanced the infiltration of rainwater during the rainy season. This recharged the groundwater supply, ensuring enough water was available during the dry season.

While these ancient cities had an impressive understanding of water management, our systems today are, of course, even more sophisticated. However, our extensive groundwater pumping across the globe has actually caused a slight shift in the Earth's rotation. This is because extracting groundwater changes how the planet's mass is distributed. Even though this change in rotation is only a few centimeters, it highlights just how deeply interconnected water is with the very structure of our planet.

So, when we think about water and its effects on our planet, there are a few key points to remember. First, water and ice have shaped and continue to shape the surface of our planet. Secondly, rain is the source of all freshwater on Earth and is essential for life. And finally, humans have, especially in recent years, significantly altered how water moves across our planet and how it's stored as groundwater. Just as it did long before humans existed, water will continue to shape the Earth and life in all its forms. From carving landscapes to sustaining ecosystems, its endless cycle will keep driving the natural processes that influence our planet.