Water is important for multiple reasons. One, it is essential for life. All humans need water in order to survive. Two, it is useful for cleaning purposes, especially in third-world countries. Water, whether it is a river or ocean, is an important mean of trade, transportation of goods, and travel. In some cases, such as Great Britain and Japan, it is a defense mechanism. Britain is nearly impossible to conquer because it is an island nation. Hope that helps!