“Catch it where it falls” is the basic idea behind:
(A) Making dams to store water
(B) Recycling of water
(C) Rain water harvesting
(D) Condensation of water vapour

Hint: To answer this question, you must recall the various methods used for the conversation of water and the basic principles behind them. Of all sources of water, rain water is the most copious and clean source of water that can be available to humans. However, the distribution of rainfall is neither assured nor uniform in all places. Thus it is important to conserve rain water.

Complete step by step solution
In option A, we have the making of dams for the storage of water. Dams use the storage of river water and then can be used whenever required or for the production of electricity through the use of turbines.
In option B, we have recycling of water. Recycling of water involves the use of already used water for another purpose. For instance the water used for cleaning of fruits and vegetables can be used for watering plants.
In option C we have rain water harvesting. This involves storing the rain water as it falls from the atmosphere onto the surface of earth. The rain water is stored in large containers as it precipitates on the earth. Thus, it involves the basic idea of catching the water where it falls. It is one of the most important and efficient ways of conservation of water as rain water is the best source of freshwater.
In option D, we have condensation of water vapour. It is simply the cooling of the vapours of water to obtain liquid water.
The correct option is C.

Note:
Rain water harvesting has been carried out since ancient times as it is an extremely efficient and convenient source of water. Many evidences of the following have been discovered in ancient structures and excavation sites.