What is Rain Water Harvesting (RWH)? It simply means catching the rain that falls on your roof or open area, and then either storing it for later use or sending it into the ground to refill the underground water.
It is cheap, simple and eco-friendly, and it is one of the best ways to fight the falling groundwater level in Punjab and across India.
Why Do We Need It?
India is facing a serious water crisis. NITI Aayog’s Composite Water Management Index report (2018) found that about 600 million Indians face high to extreme water stress.
In Punjab the problem is even more serious. We pump out far more groundwater every year than the rain puts back:
According to the Central Ground Water Board’s 2024 assessment, 115 of Punjab’s 153 assessment units (about 75%) are “over-exploited”, meaning more water is taken out than is put back. Experts say the real worry is not just how low the water table is, but how fast it is falling.
How Rain Water Harvesting Works
When it rains, water runs off the roof, flows through pipes, gets cleaned in a filter, and then goes either into a storage tank or into a recharge pit / borewell that sends it deep into the ground.
Parts of the System
🏠 Catchment area
The surface that collects the rain, usually the roof or a paved open area. The bigger the area, the more water you get.
🔧 Gutters and down pipes
Channels and pipes (G.I. or PVC) that carry rain from the roof down to ground level.
🧹 Filter / first flush
Removes leaves, dust and dirt. The first rain washes the roof and is thrown away; only cleaner water goes ahead.
🪣 Desilting chamber
A small chamber where mud and silt settle down before the water moves on, so the tank or borewell does not get choked.
💧 Storage tank
Stores water for later use. Keep the lid tightly closed to stop evaporation and mosquito breeding.
⬇️ Recharge structures
Recharge pit, trench or borewell, filled with layers of sand (top), gravel (middle) and boulders (bottom), that send water down to the aquifer.
Two Ways to Use the Water
1. Store and reuse
Collect rain in a tank and pump it to the overhead tank for gardening, washing, flushing and cleaning. Rain water is soft and free from most chemicals.
2. Recharge the ground
Send rain water through a recharge pit or borewell into the ground. This raises the water table and also improves groundwater quality by diluting salts and impurities.
How Much Water Can a Roof Collect?
You can work it out with one simple formula:
The runoff factor is the share of rain that actually flows off the roof. For a concrete roof, take about 0.8 (some water is lost to splashing and evaporation).
Roof = 100 m², rain = 25 mm
Water = 100 × 25 × 0.8 = 2,000 litres
Example 2: a whole year in Punjab
Average rainfall ≈ 534 mm
Water = 100 × 534 × 0.8 ≈ 42,700 litres per year
Benefits at a Glance
📈 Raises water table
Puts water back into the ground and helps dark (over-exploited) zones.
🚰 Saves supply water
Reduces the demand on tubewells and the municipal supply.
✨ Better water quality
Dilutes salts and impurities in groundwater.
🌱 Less runoff and erosion
Less water on roads, less flooding and less soil washed away.
What the Rules Say (Punjab)
As per the Punjab Urban Planning and Development Building Rules, 2017, rain water harvesting structures (for storage and reuse) are required for:
- all houses with plot area above 250 m², and
- all commercial and industrial buildings above 100 m².
Maintenance Tips
- Clean the roof and gutters before the monsoon starts.
- Throw away the first rain of the season (first flush), which carries the most dust.
- Clean the filter and desilting chamber regularly, especially after heavy rain.
- Keep the tank lid tightly closed to stop mosquitoes and evaporation.
- Never let dirty or sewage water enter a recharge borewell; it can pollute the groundwater.
Key Takeaways
- Rain water harvesting = collect rain, then store it or recharge the ground.
- Punjab takes out about 1.5 times more groundwater than is recharged, so the water table keeps falling.
- Main parts: roof, gutters, down pipes, filter, desilting chamber, storage tank and recharge pit/borewell.
- Water collected = Roof area × Rainfall × 0.8. A 100 m² roof gives about 2,000 litres from a 25 mm shower.
- Required in Punjab for houses above 250 m² and commercial/industrial buildings above 100 m².
- Simple, cheap and eco-friendly: every building should have it.
Sources: NITI Aayog, Composite Water Management Index (2018); Central Ground Water Board, Dynamic Ground Water Resources of Punjab (2024).