There are some countries that roof rain reservoirs are common. I heard about Sydney for example. However such practices suffer from some water quality issues. The harvested water need to some purification if it is intended to be used as drinking water. Some heavy metal pollution were detected in their roof pavement but this kind of heavy metals can be removed maybe using active nano-tissues.

To avoid cost factor and also to make it simplistic, one of the best way is to concentrate on existing drain pipe outlets or any natural point of roof water outlet, and catch hold  the water at this particular point, leaving aside all other complicated set up. One can be just concentrate from this outlet point to a low cost storage space located nearby (may be a covered depression, a tank made of any material etc). Conveying rainwater from that outlet in a regulated manner (channel, pipe etc) and passing it through a layer of charcoal mixed strata to make it relatively purify and then storing with least loss via infiltration or evaporation, is a best and most economical way of roof top rainwater harvesting. If quality is good, it can be used even for drinking purposes. If quality it relatively poor, it could be beneficially used for kitchen gardening or domestic utilization like utensil washing/cleaning and animal's utilities etc. Any type of roof (even the thatched roof of straw too could yield ample volume of rainwater harvesting & utilization.

please contact Mr. A R Shivakumar, Senior Fellow, Karnataka State Council for Science and Technology, IISc Campus, Bangalore 560012 India. Email: [email protected]

Phone No. +91 80  23341652

Thank you all for your answers and they are really helpful to me.

Now days awareness about rain water harvesting is increasing. There are different traditional as well as scientific methods for different regions suggested by scholars. number of research papers describes such methods.

Rain water harvesting in India is still like a bookish term only in reality it a high hanging fruit.

To cope with water demands of consistently increasing population and erratic rainfall patterns water harvesting at household level is need of the day especially in areas where there is very limited sources of water supplies or ground water is very deep. There are basically two ways of rainwater harvesting

1. Collection in a storage tank preferably below ground, for house hold drinking consumption during the year, the technique being used in some parts of India since centuries

2. Diverting the rooftop water or clean surface runoff water to groundwater to groundwater aquifer

However, it is most important to take all precautions that rain water shouldn't get polluted before it enters the under ground aquifers.

Making Rainwater Harvesting a Key Solution for Water ... - MDPI

www.mdpi.com › pdf

PDF by Q Qi - ‎2019 - ‎Related articles Oct 11, 2019 - Thus, rainwater harvesting systems entailing carefully harvesting, storing, ... Sustainability 2019, 11, 5606; doi:10.3390/su11205606

This link gives a detailed explanation of the methods

https://theconstructor.org/water-resources/methods-of-rainwater-harvesting/5420/

In some rural areas in South Eastern Nigeria, household methods commonly in use for rain water harvesting include Surface runoff harvesting and Roof top rainwater harvesting.

Article Sustainability of Rain Water Harvesting System in Terms of W...

good question