Sources of fresh water

Surface water

Although the only natural input to any surface water system is precipitation within its  the total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificial, the permeability of the  beneath these storage bodies, the

Natural surface water can be augmented by importing surface water from another watershed through a or  It can also be artificially augmented from any of the other sources listed here, however in practice the quantities are negligible. Humans can also cause surface water to be "lost" (i.e. become unusable) through 

is the country estimated to have the largest supply of fresh water in the world, followed by nd

characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water lost.

Human activities can have a large and sometimes devastating impact on these factors. Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing stream flow.