A drop’s journey

Water is always moving between the land, the sea and the air. This repeating journey is called the water cycle. The Sun provides energy that helps drive it. Imagine a drop of water in the Tasman Sea. As sunlight warms the sea, some liquid water changes into water vapour, an invisible gas, and rises into the air. This change is called evaporation. The dissolved salt stays behind, so evaporated water vapour is fresh. Higher in the sky, the air is cooler. The vapour cools and changes into tiny liquid droplets. This is condensation. The droplets gather around tiny particles of dust and form clouds. Clouds are made of water droplets or ice crystals, not water vapour. When droplets or ice crystals grow too heavy to stay in the air, water falls as precipitation. It may fall as rain, snow or hail. In Aotearoa New Zealand, rain can run over the land into streams and rivers. Some water soaks into the ground and becomes groundwater. Plants can take up some of this water through their roots. Rivers carry water back towards the sea. Some water also evaporates from lakes, soil and plants. Then the journey begins again. A water molecule may follow different routes, and the journey can take a short time or a very long time. The water cycle has no single starting point: it is a connected system that keeps moving water around Earth.

Read closely