Rainwater Harvesting: Methods and Benefits

In a world of shrinking groundwater tables, letting rain flow into the drain is a crime. Rainwater Harvesting (RWH) is the simple act of collecting rain from surfaces (like roofs) and either storing it for use or diverting it back into the ground.

The Math: How much can you save?

The formula is simple: Harvest = Area (m²) × Rainfall (mm) × Runoff Coefficient (0.8)

(Note: Concrete roofs have a coefficient of ~0.8-0.9. Garden soil absorbs water, so it has a low coefficient of ~0.2)

Components of a System

1. Catchment & Conduit

The roof is the catchment. PVC pipes are the conduit.

• Tip: Keep roof clean. Avoid chemical waterproof coatings that leach toxins.

2. First Flush Diverter (The Gatekeeper)

When it rains after a long dry summber, the first 10 minutes wash down bird droppings, dust, and leaves. You DO NOT want this in your tank.

• Mechanism: A simple vertical T-pipe. The dirty water falls into this "dead end" pipe first. Once it's full, a floating ball seals it, and the remaining CLEAN water flows over into your tank.
• Reset: You open a small valve at the bottom to drain the dirty water after the rain stops.

3. Filtration

Before storage, removing fine silt is crucial.

• Gravel/Sand Filter: A masonry tank with layers of big gravel (bottom), small gravel (middle), and sand (top).
• Vortex Filter: Uses centrifugal force to spin out dirt. Good for industrial pipes.

4. Storage or Recharge?

• Store: If you need water for flushing/washing.
• Recharge: If your borewell is dry. Directing filtered rain into a borewell acts like an IV drip for the earth, raising the water table locally.

Pre-Monsoon Maintenance Checklist

Do this every year in May/June:

• Clean the Roof: Sweep away leaves and silt.
• Check Gutters: Ensure no blockage or bird nests in the pipes.
• Empty First Flush: Ensure the diverter valve is not clogged.
• Wash Filter Media: If using a sand filter, scrape off the top 2 inches of dirty sand and replace/wash it.