Surface water is water on the surface of the planet, above the ground. It is the water in rivers, lakes, wetlands and oceans. It is different to groundwater, which is in the soil, and atmospheric water, which is in the sky.
Fresh surface water is added to by precipitation and by taking ground-water from the ground. It is lost through evaporation, where it becomes atmospheric water, or through seepage into the ground, where it becomes ground water. It is also lost through use by plants for transpiration, animals for drinking, or by humans for agriculture, washing and other purposes. Fresh water is also discharged to the ocean, where it becomes salt water.