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South Asia Rainwater Network (SARNET)

3rd International Conference of SARNET on

Conserving Blue Diamonds: Creating Climate Resilience through Rainwater Conservation and Management

23rd - 24th of September, 2025 Expo Centre, Lahore, Pakistan

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From Orbit to Aquifer; Space Technology for Rainwater Harvesting

Khalid Mahmood

Institute of Space Science, University of the Punjab

Remote Sensing, GIS and Climatic Research Lab (RSGCRL), Center for GIS and Space Applications

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Open-source solutions

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Rooftop Rainwater Collection

Such a system involves a direct collection of rainwater into storage tanks. Implementing such a system has several challenges that a space-based GIS system can address comprehensively.

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Mixing of impurities in rainwater

    • Impurities from air:

Dust, pollen, particulate matter, industrial emissions, vehicle exhaust etc.

    • Roof surface:

Bird droppings, dust, leaves, organic debris, chemical residues from roofing materials, and microbial growth due to stagnant water or organic buildup.

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Removing these pollutants is mandatory for making the water safe for drinking. There are several treatment and purification methods including chlorination, boiling, activated carbon filters, sedimentation tanks, UV sterilization, or reverse osmosis filters etc. Many of these filters can be made locally but selection of the treatment method depends on types of pollutants that vary geographically and seasonally and needs to be determined.

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The Storage Tank

Size of the Tank:

The size of storage tank depends on the amount of rainwater received (varies locally) and size of collection area (rooftop). This requires temporal track of precipitation in a region.

The rainfall data is also important for quantifying the purity of rainwater, as the month with a little rainfall gives more polluted water than the month with extensive rainfall.

Type of the Tank:

Type of the tank usually comes with the economic suitability. Plastic tanks are a ready-made solution but its transportation to remote areas is very expensive, so their suitability zone is urban areas and its outskirts. The other option include Ferrocement tanks that can be built on the spot (with a low cost of material transportation) with huge sizes to store even thousand of gallon water. The two famous types are Kalabashi Tank and Pumpkin Tank

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Space Based data sources

There are global repositories of air quality and precipitation, developed using both space and ground based measurements.

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    • Global rainfall repositories provide rainfall patterns, average precipitation, months of maximum rainfall in a specific region that can help communities to estimate the suitable tank size and time of the year with best quality of rainwater as well as to meet the water demand during both wet and dry seasons.

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    • Global air quality repositories provide details of particulate matter, volatile organic compounds and other contaminants in the atmosphere.

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The model will be implemented in GEE amd made available to communities through GEE App where they can just provide the shapefile of their rooftop of draw it on the interactive interface to get

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    • Size of Tank they need
    • Type of Tank they need
    • Best time of the year to store water for drinking
    • Filtration Requirements
    • Indigenized Filter available
    • Feasibility of the Rooftop rainwater collection system
    • Cost benefit analysis of the Rooftop rainwater collection system

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Potential Outcomes

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Thank You