Willie the rain drop began his day like any other: among the clouds. He was a water droplet, you see, made up of many many water molecules called H2O. 

Willie floated along with the wind, relaxing. He collected more water molecules as he went along. He became bigger, and bigger, and heavier, and heavier.

As raindrops form and grow large up in the atmosphere, they begin to stick together to create clouds. This is called condensation. There are several different types of clouds. This big cloud that Willie finds himself in, is a cumulonimbus cloud. This type of cloud produces thunderstorms and heavy rains. Willie felt very heavy!

A big storm began, and Willie fell down to the ground. He brought all his new friends with him. When the water in the sky falls down to the ground, it is called: precipitation. Willie and his friends made themselves right at home.

As raindrops such as Willie find themselves down on the ground they begin to flow together along city streets, gutters, ditches, and gulleys. This is called runoff. The water is searching for a place to go.

The runoff will end up in a stream or a creek. Willie and his friends bring with them anything that they pick up along the way, such as chemicals that are harmful to the environment, or rubbish and garbage that don't belong in nature.

The streams and creeks will end up feeding into rivers. Sometimes, water ends up in lakes and ponds as well. These resources provide drinking water for people and animals, as well as habitats for many plants and animals.

The rivers empty into the Earth's oceans. This is the end of the journey for many rain drops such as Willie.

The oceans hold the majority of the planet's water supply, and they support a vast array of plants and animals. The oceans also stabilize our weather patterns and the temperature of the Earth.

Sometimes, when it is quite cold, Willie and his pals come down as frozen precipitation. This may be in the form of snow, sleet, or hail.