Designing a gravity filter for rainwater harvesting system in Tiruchirapalli, Tamilnadu

Dear Members,

Kindly go through the following particulars of a planned RWH system:

1. Location: Tiruchirapalli, Tamilnadu
2. Activity: Construction of filter unit (inline filter)
3. Purpose: drinking water for panchayath union school,
4. Harvesting rainwater from rooftop of school
5. Type of roof: RCC
6. Rainfall:751mm
7. Intensity of rainfall: 80mm/hour
8. Harvesting potential from roof area:2500
9. Storage capacity : 30,000 litre

For the above particulars, I want to design a gravity filter system (using filter materials like sand, charcoal,pebbles and gravel, kept as vertical layers). What should be the size of filter unit and thickness of each filter material and rate of infiltration? for the mentioned particulars.

Myla Nayakam