Gravity: Nature's Tool for Moving Water Over Long Distances

Water flows naturally over long distances if a single condition exists: The elevation at the beginning location is higher than the elevation at the ending location. The force of Gravity naturally moves water from higher to lower elevations.


Human Settlements Around Nature's Rivers

The River Nile
Source - abbaymedia.com

Running downhill, rivers deliver water to communities all along its length. 
The longest river, The Nile, is over 6,600 km long 
Traversing this distance, the Nile sustains communities of life in ten countries, namely, Ethiopia, Eritrea, Sudan, Uganda, Tanzania, Kenya, Rwanda, Burundi, Egypt, Democratic Republic of Congo and South Sudan.
The Nile originates at an elevation of 2,700 m (above sea level) and ends in the Mediterranean sea after its 6,600 Km journey.
The Nile and the other rivers contain an estimated 0.006% of all the freshwater on Earth. These 509 cubic miles of freshwater are regularly replenished by the hydrological cycle.


Human Settlements Away From Rivers and Lakes
Gravity is the first natural force that humanity learned to harness to bring water from a river or a lake to a human settlement.
Surface Structures
The first known successes by humanity to use gravity for irrigation were in four regions of the world: In Egypt around the Nile river, in Mesopotamia around the Tigris and Euphrates rivers, in India around the Indus and Ganges Rivers and in China around the Huang He (Yellow) river.
The larger channels feed water into the smaller and smaller channels using the force of gravity. The channel beds have to be sloped correctly for gravity-fed water to move from channel to channel. 
This method of irrigation, known as furrowed irrigation, is still widely used in the world. It originated as early as 5000 BC.
Underground Piping

Source - en.wikipedia.org

The puquios in Peru, use gravity to channel surface water into pipes dug out under ground by humans, that end at a settlement. Peru and the many other human communities in the Andes Mountains, used this method extensively to channel water into pipes.
Arranging a number of puquios to feed into a single pipe is said to have provided enough freshwater for a community of over a hundred people.