The water cycle is the movements of water above, upon and below the surface of the earth. This cycle has 4 stages that are : storage, evaporation, precipitation and runoff. These stages are often cyclic.
Water is stored in lakes or within the ground, it evaporates in high temperature and creates clouds then precipitates back to the earth and the cycle starts again.
In a permaculture system that has large trees, ponds and ground cover this water cycle fits firmly with the ecosystem. Trees keep ground cover protected to help retain ground moisture, ponds store the water and provide sources of evaporation. Precipitation occurs and runoff keeps ponds and waterways filled with new, fresh water and the soil with renewed moisture. Deserts have few trees and little rain whereas a rainforest is full of trees and it rains regularly. An environment in balance can easily be disrupted through over consumption of resources and the pollution of water and can turn a flourishing system into a struggling waste.