Rainwaterharvesting.org

Rainwater harvesting is an option which has been adopted in many areas of the world where conventional water supply systems have failed to meet the needs of the people. Examples of RWH systems can be found in all the great civilisations throughout history.

Here's an eToolkit on rainwater harvesting that tells you all that you need to know to harvest rain successfully.

The http://rainwaterharvesting.org site has a map of Delhi showing geology, water level, water quality and giving recommendations for rainwater harvesting in different areas.

View the map here: http://www.rainwaterharvesting.org/index_files/intro_map.htm

The information may be out of date.

Image source: http://rainwaterharvesting.org

This section from www.rainwaterharvesting.org deals with traditional water harvesting systems. Water has been harvested in India since antiquity, with our ancestors perfecting the art of water management. Many water harvesting structures and water conveyance systems specific to the eco-regions and culture has been developed.

• They harvested the rain drop directly. From rooftops, they collected water and stored it in tanks built in their courtyards. From open community lands, they collected the rain and stored it in artificial wells.
• They harvested monsoon runoff by capturing water from swollen streams during the monsoon season and stored it various forms of water bodies. 
• They harvested water from flooded rivers