How much rainwater can be collected in a day from 100 square meters. roof? Enough to accommodate a family of four for at least 3 days
Detached apartments, gated communities, shopping malls and other buildings with huge surface areas can harvest thousands of liters of rain. (Image for representation purposes only) | Image source: SS Kumar
It has been raining in and around Hyderabad for the past few days. Can it be used for home purposes? People working for rainwater harvests say that if 25mm of rain is received, about 2,000 liters can be collected from a roof spanning 100 square meters (more than 1,000 square feet).
According to the Telangana Development Program Association, on the morning of May 16, 2025 (May 16, 2025), Golconda received the highest rainfall of 36.6 mm. Detached apartments, gated communities, shopping malls and other buildings with huge surface areas can harvest thousands of liters of rain.
The amount of water required for a day
Kalpana Ramesh, founder of the Rainwater Project, said a person needs 130 liters of water per day. At least three days, about 2,000 liters of harvested rainwater is enough to accommodate a family of four.
How can rain be collected from calculated roofs?
The amount of rainfall that can be collected from the roof is calculated by the surface area compared to the amount of rainfall
As the type of roof surface (vegetation or hard), slope, debris, rainfall, precipitation and other factors affect the collection of rainwater, the calculation also includes runoff coefficients.
The 0.8 coefficient means that 80% of rainwater can be collected
Formula: Surface area (square meter) x rainfall (in meters) x runoff coefficient
Example: If the rainfall depth is 25mm, over 100m2 roofs, the collected rainfall is: 100m2 x 0.025m2 x 0.8 = 2 cubic meters (2,000 liters)
Groundwater level 1 in Hyderabad
As the annual average level of the Greater Hyderabad Municipal Corporation (GHMC) continues to fall dangerously, it has dropped by 11.40 meters underground (BGL) from 2018-19, and its annual average level continues to fall to 8.98 in 2024-25. 9.05 to March 2024 – 25. It continues to be in the red zone – the BGL is below 20 meters.
Areas of the outer loop of the groundwater level in the red area include Malkajgiri, bachupally, Dundigal, Serilingally, Hayatnagar, Abdullapurmet, Saroornagar and Kukatpally Mandals.
Filters can be used
Vishwanath Srikantahiah of Biome Environmental Trust said sewage treatment for storm water can also be used to store storm water. He said the roof must be made clean. When there is rain forecast, the roof can be cleaned. A filter that costs about Rs 3500 can be used to filter rainwater.
Ms. Kalpana said the inline filter is installed in the storm water pipe. It removes leaves and other debris before the collected rainwater is placed in sewage or RWH pit.
It rains all year round
She said that since rainfall is not limited to monsoons, people will also have enough water in non-monsoons. According to TGDP, from June 1, 2024 to May 15, 2025, the cumulative rainfall of GHMC was 996.5 mm, and the normal resistance was 811.8 mm.
A contractor said it would take about Rs 15,000 to build an RWH pit that is three feet wide and four feet deep, which requires maintenance.
publishing – May 19, 2025, 5:06 pm IST
