About 3,000 mm of rain falls on Goa in an average year (Goa/Panjim long-term climate normal) - most of it in just four monsoon months. Catching even part of it changes the dry season completely.
This is the basic idea of rooftop rainwater harvesting. The calculator below estimates how much rain a roof could collect over a year - actual storage depends on tank size, overflow and when the rain falls, and filtered rainwater is not automatically safe to drink.
Gutters guide roof rain through a filter into a storage tank. The first dusty rain is automatically kept out.
A pit filled with layers of gravel and sand slows water down so it soaks into the ground instead of flooding streets.
Soil sensors open drip valves only when the ground is actually dry - farms save 30-60% water this way.
Water from showers and basins is lightly filtered and reused for gardens and flushing, cutting fresh demand sharply.