10.3.2.1. Roof top rain water harvesting (RTRWH)

It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, and the rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to an artificial recharge system. This method is less expensive and very effective and if implemented properly helps in augmenting the groundwater level of the area.

Roof Top Rain Water Harvesting (RTRWH) refers to the practice of collecting rainwater that falls on rooftops. When rain falls, it collects on the roofs of buildings, which are considered catchments. The harvested rainwater can be stored for later use or directed to recharge groundwater. This method is affordable and highly efficient, especially when properly implemented, as it contributes to increasing the groundwater levels in the surrounding area.

Imagine a sponge soaking up water from a spilled drink. Just like a sponge absorbs water, rooftops can capture rainwater. If you have a bucket under the sponge, you collect all that water to use later. Similarly, RTRWH helps communities catch rainwater from roofs, allowing them to use it for watering plants or even for drinking after it’s purified.

The system mainly constitutes the following sub components: Catchment, Coarse mesh, Gutters, Conduits or Conveyance, Transportation, First flush, Filter, Storage, Supply unit.

The RTRWH system is made up of several key components. These include:

• Catchment: The surface collecting the rainwater (like rooftops).
• Coarse Mesh: A filter preventing large debris from entering the system.
• Gutters: Channels that carry the collected rainwater from the catchment.
• Conduits or Conveyance: Pipes that transport rainwater to storage.
• Transportation: The methods used to move rainwater from gutters to storage.
• First Flush: A system that diverts the initial dirty water runoff from the first rainfall before clean water can be collected.
• Filter: A device to clean the water further before it's stored.
• Storage: Tanks or containers where the collected rainwater is stored for future use.
• Supply Unit: The mechanism that allows the use of the stored water.

Think of the RTRWH system like a well-organized kitchen for cooking. The rooftop acts as the pot where ingredients (rainwater) are collected. A fine mesh strainer is used to remove large lumps (debris) before pouring it into a pot (the storage tank). Just as you would separate the ingredients before cooking, the first flush system cleans out dirty rainwater first, ensuring clean 'ingredients' are cooked (used) later.

The catchment of a water harvesting system is the surface which directly receives the rainfall and provides water to the system. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanized iron or corrugated sheets can also be used for water harvesting.

The catchment area is where the rainwater first falls and is collected. This could be various surfaces such as:

• A flat rooftop, being ideal when made from materials that allow efficient collection.
• Courtyards or paved areas, which can also channel rainwater towards collection systems.
• Open ground or lawns, though less efficient, they can still collect rainwater in certain conditions. Materials like reinforced cement concrete or corrugated sheets are preferred for rooftops because they are durable and effective at directing water into the harvesting system.

Think of the catchment like a big, wide sponge placed outside during a rainstorm. The materials you choose to make your rooftop (like RCC or galvanized iron) determine how quickly and efficiently the sponge collects water. If it’s a clean, flat surface, it will soak up and direct that water easily into your system, just like a sponge would soak up all the surrounding water.

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