Dear Paresh,

Yes you are correct that now a days many governments make it mandatory and it should be. We should plan to have "Rooftop Rainwater Harvesting System" in every possible house and should use that harvested water in that area itself. 

My intention was not like that. After having 21 years experience about the subject, I am quoting this because I am intend to say that this is a ideal size of the catchment for the said areas and in between we have to think about the semi-arid area also and also for high intensity area, i.e. high rainfall area. With the told catchment area we could have a better result.

Thanking you,

Dear Prakash,
Welcome to the forum.

As you may already know, many local governments now mandate property developers to harvest rainwater. You said

The survey of catchment area and from my experiences it should be minimum 100 M2 in the area where the annual average rainfall is greater than equal to 1,350 mm. and for arid zone where the rainfall is less than 700 mm. the catchment should not be less than 200 M2

Do you imply that rainwater from rooftops measuring less than 100 or 200 sq m should not be harvested or is it not feasible in your experience? 

Perhaps, videos (like one below) by Vishwanath aka Zenrainman would interest you


Regards
paresh

Dear Ross Bowen,

It seems, you are quite a experienced fellow in water resource sector. Thanks a Lot for your comment. You are saying about something double way of filtration. This is very much needed for conserving rainwater for human consumption and as well as for groundwater recharge. Here I am designing doubly activated carbon filter as per site condition. This is I think same as you mentioned, is not it? In India the annual average rainfall varies from 100-11,861 mm. So, we have to think about the same at the time of implementation.

Thanking you with best regards,

Prakash

Rainwater Harvesting is widely used in Australia in both cities and regions. My family has been living on rainwater for 50 years even though we have a mains water supply. We prefer the rainwater and use a 2 stage underbench filter to polish what is a good and healthy method of water supply. The irony is our towns and cities are being subject to water restrictions in these climate change environments.
Benefits are enormous and my dream for the future is that this will become mainstream and the disposal of our wastes are recyled and returned to enrich our barren soils via urine separation and solids composting. 

Natural Water Resource Management through Rooftop Rainwater Harvesting is the technique through which rain water is captured from the rooftop catchments and stored in a designated reservoir. Harvested rainwater can be stored for future use and in subsurface groundwater reservoir by adopting artificial recharge techniques.
 

• The survey of catchment area and from my experiences it should be minimum 100.00 M² in the area where the annual average rainfall is greater than equal to 1,350 mm. and for arid zone where the rainfall is less than 700 mm. the catchment should not be less than 200.00 M².
• The catchment should have rectify measures if required
• The down gutter drain in the roof should be well designed
• Can be channelize through one filter or two depending upon impurities

As rainwater is usually free from impurities except those picked up by rain from the atmosphere, but the quality of rainwater may deteriorate during harvesting, storage and household use. Generally, as a practitioner I came to know that it is free from many chemical & bacteriological contamination; as a result of that we could able to use that for consumption with a minimum treatment. We should think about the same.